Hopefully by now you have a decent understanding of how you can reshape your seat to make it more comfortable, and why this will work. Now it's the time to remove and reshape some of the stock foam, and to add and shape some new, more comfortable foam. In the end, you're looking for optimum pitch, cradle, and support.
This part of the process can be a bit disconcerting the first couple of times. You may wonder whether you've ruined your seat. Just realize that, unlike modifying an internal engine component, you can't do any damage to the bike here. It's just a seat, with some foam and a vinyl cover. As you try different combinations of the suggestions below, you'll quickly gain confidence in your ability to master the art of seat-improvement.
Note that the descriptions below should be viewed as OPTIONS, not steps that must be followed exactly as described. Be creative and to try out approaches that you think will work best for your bike, body, and riding style. You might want to try just some of the modifications described below. You can always try a "version," put the seat on your bike, give it a try, and then adjust as necessary. The Other Ideas page has a couple of other ideas available to you out of the almost infinite variety.
With the seat cover removed, you should have plenty of access to the area that you'll be working on.
These pictures outline the basic plan of attack. The key changes shown here are reducing the forward pitch, increasing cradle and, increasing the length of the driver's platform to give taller riders a bit more forward-backward room.
Also, notice that we'll be using two layers of foam. The bottom layer provides a firmer foundation layer, while the top layer uses softer foam to improve comfort and minimize any imperfections in the shapes below it.
It may help to mark the basic areas of the stock seat that you want to grind lower. Just remember that it's generally easier to remove foam than to add it, so work patiently and carefully.
Carefully grind down the areas of the stock foam that you've identified. Use very light pressure with the grinder, as it easily cuts through and takes off foam. Use longer strokes where possible, instead of working the grinder in one small area. Never push the grinder into the foam in the direction of its rotation; instead, pull it towards you, gently "sweeping" away the foam you want to remove.
Always use eye protection and a filter mask when grinding foam. Grinding foam can kick up a lot of dust that can irritate your eyes and lungs.
Occasionally check the area that you're grinding with your hand to make sure there are no accidental, significant high or low spots. If there are, gradually remove them with the grinder.
While you're grinding down some of the stock foam, you may want to dish the surface a bit to improve cradling. The back part of the driver's platform on this Honda VFR seat (pictured below) needed to be taken down as far as the seat pan to mitigate the pitch angle and improve cradling. Removing this much foam doesn't pose a problem since I'm adding about 1 1/2 layers of quality foam on top of this area. Also, very little weight is supported in the very back area area of the driver's platform.
The before-after pictures above bring up a good point: sometimes the shape of the stock seat pan and stock amount of foam doesn't offer much opportunity to grind down enough foam to make substantial pitch or cradle changes. This may cause other modifications to increase the seat height a bit, though this depends on the specific combinations of modifications made. It's a trial-and-error process that will be different for each bike and rider.
In this particular case, I was able to reduce the height of the rubber bumpers under the seat pan. This reduced the forward pitch of the stock seat slightly. I didn't want to completely remove the bumpers since they absorb some engine and road vibration, and also to prevent the seat pan from grinding on the rear cowl plastic.
Adding some width in the area that bears most of a rider's weight will help cradling and comfort. About the most that can be added without changing the seat pan is about 1 1/2 inches beyond the stock width. Adding too much extra width also will make re-using the stock seat cover more challenging.
The pictures below show one way to do this. Cut out a section of the stock foam. Using spray adhesive, place a piece of rebond or firm closed-cell foam in the cut out section. I like using 1" thick pieces of foam, since they're easier to cut and shape. If you want a thicker, 2" piece, all you need to do is laminate (i.e., glue) two 1" pieces together using spray adhesive.
As seen in the last picture in the sequence, it helps to add and shape a small piece of foam to smooth out the overall shape and add a bit more support under the "cantalever" or part that sticks out. Exactly where you add width to the seat depends on the your body and personal preferences. The pictures below are illustrative only.
One or two pieces of 1" open-cell foam can be used to build up the nose. This improves both cradling and reduces forward pitch. This can really help minimize the obnoxious-sliding-into-the-tank syndrome. If you use two pieces of 1" foam, just glue them together with spray adhesive. Then glue these onto the stock foam. Though 2" may seem like a lot of extra height at the nose, the material is a softer, open-cell foam that compresses nicely under pressure, and I've found this additional height necessary to mitigate the uncomfortable forward pitch and poor cradling of most stock seats. Also, you'll be adding additional foam on the seat later, which effectively will make the rise in the nose less pronounced. When you try it out for a bit on the road and you find it's a bit high, you can always grind down small amounts of ore foam until the nose is just right for you.
Grind this added piece of nose foam into a smooth shape that's comfortable for you. When shaping them with the grinder, make sure that the grinder wheel rotates towards the seat so that the two pieces of foam stay tightly together. Otherwise, you could easily pry apart the two pieces with the grinder as you're trying to shape it. Be patient and take off small amounts at a time. Work your way around the shape, rather than concentrating on one small section at a time. When you're finished, the shape should be smooth, balanced, and with a tight seem.
This step adds a 1" layer of high quality, firm foam to the seat platform. This replaces the less comfortable stock foam that was removed, and adds back some of the height that was lost. This additional layer also provides a foam layer that can be further shaped to improve pitch and cradle. For this layer, you can use firm open-cell foam (such as rebond) or a firm closed-cell foam.
Notice how the area around the nose is feathered down. This keeps the nose of the seat feeling softer and not getting too high. If you want to use this layer to decrease the pitch of your seat a bit more, grind down the rear part of the seat platform. Grinding down the center part of the platform, as shown in the picture, can also increase cradling.
I've found this step to be very helpful in calming the sitting bone (ischium) hot spots. The step involves the removal of a 1" piece of firmer foam (e.g., rebond, B in the pictures below), and replacing it with a 1" piece of softer foam (A in the pictures below). The softer foam could be the same type of open-cell foam that you used on the nose. If you use a good quality open-cell foam, the two layers of it under your sitting bones will not cause excessive "ride." In other words, it shouldn't be so soft as to cause you to sink way down into the seat.
Sit on the bike with the seat attached. Notice where your sitting bones make the most contact with the seat. Use white chalk, pastel, or something similar to mark this area on the seat. You can cut out the marked area with scissors, utility knife, or something else. The cut out area(s) are labeled as B in the pictures below. If you use scissors, you'll first have to remove the piece of foam from the seat.
Now cut out a piece(s) of the softer foam (A) so that it fits into the hole(s) you just cut out (B). Spray a bit of adhesive where it will set, and put it in place.
What this will do is give you a bit softer area where your sitting bones make contact with the seat. On longer rides, the weight on these bones, if the seat is not properly shaped or too firm, can really start to ache.
This step involves putting a 1" piece high quality, open-cell foam over the whole seat platform. This will give the seat a slightly softer feel than if you left the firm rebond or closed-cell foam on the top layer. This final layer will also cover up surface imperfections, making the seat look and feel smooth when you re-install the seat cover.
This step doesn't involve much other than cutting the piece of foam to the correct shape. You may want to slightly smooth out the corner edges with a grinder, and also feather a bit the front edging where the hamstrings contact the front/side of the seat (see pictures below).
Couple of Videos
Sometimes watching someone else do this job can be a big help, even if the specifics of the project and tools used are different from yours. If you don't know someone who's good at this, the next best thing is a video. Here are some videos that simply let you watch others work with foam.