Within the past few months I've done a lot of bodywork on my Dart, and started painting it (with a roller and rustoleum). Here are some pics where you can see the bodywork. If you look closely at the car with paint on it, the bodywork aint *perfect*, but it's pretty good for a goofball in his garage and most people would not notice any issues. If I had painted it black it would be another story..
http://www.flickr.com/photos/xit1965/sets/72057594131616795/
If all you have is those few dents, you're lucky but I suspect you'll find more and more just like I did. Get yourself a nice longboard (17.5" I think), and I heard another great tip on here which is to make a whip out of a clothes hanger. Basically fold it into a loop with a handle (wrap some duct tape around the handle) so that you can smack the sandpaper with it to remove some of the buildup.
I prefer using 80 grit while the bondo has begun to harden. 60 or 36 grit tends to scratch up the neighboring area quite a bit, whereas 80 is a bit more gentle and you can feather it with 180 grit after that.
Also get yourself some fiberglass resin. After your final coat of bondo where you think it's OK, cover the whole area and beyond with a THIN skim coat of fiberglass resin mixed with bondo (then of course the bondo hardener). It takes longer to setup that way, so I always just let it dry for a few hours. Then start with 80 grit, then 180 then 240 and beyond. Mixing the resin in will prevent pinholes and fills in tiny scratches really well. Also the skim coat will look wet when you apply it, so you can see if it's wavy or not.
One more thing, I used the cheap Bondo and know a veteran bodyman who uses the cheap bondo for his home projects too. I'm not going to say I ever tried the "good" stuff, but when I went to buy some and saw the price tag, I figured I'd just stick with what got me there.
Also you may want to avoid any power sanding tools, they can just do damage faster..
Good luck!
edit, here's a good before and after. Luckily those high spots dont stand out too much with paint..