-reduce the picture size (duh), and:
-erase some frames, like if there are 10 frames then I delete frame 2,4,6,8,10
These are the most important, you should have some mercy on other people's bandwidth and do these for every single gif you make. Sorry, I die a little every time I see someone posting a five-second gif that's over a megabyte, when about one minute's worth of optimization could have cut it in half without losing quality.
There's more you can do, say hello to the IR optimization pane:
- Optimize the palette. IR defaults to the maximum color count (256) when in fact you almost never need that many. If you have a lot of time and patience, you can really go nuts with this and manually pick only the colors you need. Most of the time though it's enough to let IR decide which colors to prune. The easiest way is to try dropping the count from 256 to 128; if it looks bad increase it a little until you find a setting you can live with, otherwise keep going down until you can't cut anymore without dropping a vital color.
- Adjust the dither. Dither can be good in that sometimes you can lower the color count by rather a lot and it will mask the effect. Other times it's best to scale it down or just turn it off. My advice is to play around with it to see what looks best, you can usually shave off a few kb by experimenting with dither.
- Increase the lossy. I'm willing to bet that there's not a person alive that can detect the difference between a gif at 0% lossy and one at 5% with the naked eye. It's not much of a difference in terms of size but it may be just enough to get an avatar under 50kb or whatever.
- Remove redundant frames. This isn't usually an issue when you're working with a live-action source, but if you're cutting from other stuff (like Flash animations or cartoons) there will probably be several identical or near-identical frames. If you have a double, junk the first one and double the delay on the second. No one will ever know the difference. Open this gif in IR and look at the frame delay, you'll see where a ton of redundancy was cut:
This is way more than I meant to type so I'm gonna stop now.