One thing I have found when it comes to body filler, is that every different kind seems to be quite a bit different. I know where I am at, there are many different auto supply stores, and most every one has a different brand filler. I highly recommend you go through and try all the different kinds, that is if you do enough of this kind of work. Personally I always buy the lightweight filler from Napa. It is the cheapest out of all the brands I have used, and it seems to be the best all around filler at the same time. This is of course dependent on what your using it for, but it has to have good consistancy and it needs to sand easy. This does both for me. One other thing I recommend that most people don't do... Sand BEFORE the filler is completely dry! I normaly lay a layer of filler down. Go over it a couple times with a heat gun. Right as it gets to the point where its "half hard" (point where you can still cut it with your finger nail) start sanding.... This takes a lot of time off of your sanding. You will go through a little more sand paper if your not good at estimating when to start sanding is the only downfall. Of course this only works when your doing the rough sanding at the start of the project.

There are also many practices that come into play when you want to do a really good job with the finish sanding of a project. The finish sanding of a project is probably one of the most important steps to make something look really nice. A few of the tricks I have learned are as follows.

First tip, always use sharp paper in these last few sanding steps. Click the conservative switch down a couple notchs.

Second tip, cover the project completely with a THIN layer of filler. Why you do this is simple. When you're sanding, you are trying to make something straight and/or seemless as possible. To do this you must sand one solid layer of the same material. For example, if you had a project made out of fiberglass, and you layered half of it with filler. When you're sanding on it, it will be near imposible to sand both sides equally. It doesn't really matter how good of a sander you are, the materials are a lot different when it comes to how they sand. This will make it really hard to hide the seam. If you want it really nice, you don't even want different layers of the filler to show since they hardened at different rates, etc.. So, if you are trying to make a peice as close to flawless as you can, you must make it so the whole area your sanding sands equal. To do this you must have the same material over the whole section. Of course your likely going to have to feather this into an edge somewhere. You just need to make sure that the area you feather it in will not be as critical, or make sure it's in a place you can hide. A good example would be if your sanding one large flat surface. You don't want the line where the bondo/fiberglass (or whatever material) meet being right down the center of the peice, but rather at a corner or edge of some sort.

Third tip, always try to sand in one direction. You do this because it keeps all the sand scratchs going one direction. This helps, because you can tell much more easily what sections need to be sanded and how much. The second part to this tip, when you do the next layer of sanding, sand at a 90degree angle to the last time. This allows you to see much easier where you have sanded, and where still needs more. It just makes the low spots stick out more (works even better when used with the next tip).

The last tip, buy one of the black powder pads. Not sure on the technical description/name on this. They look like a big makeup pad. You use it by putting a colored powder on the pad, then wipeing it over the project. What it does, is make it much easier to see what parts of the peice your working on are actually being sanded. So after you put the powder on, you sand lightly over the whole project. Any spots that are low will have colored powder remaining on them, since the paper won't sand it away. This product is very helpful when the peice is getting near completion since it gets hard to see/feel low spots. The only problem is this part is easy to cheat, but obviously that won't help. GO SLOW!