Taking over planets

Are you talking about the militia forces that are initially there or wresting control of it from another player?

Militia forces, on like the 2nd or 3rd planet that I take over.  I can kill them, but they seem to kill 1 or 2 LF's from time to time.  Do most people teleport them out, or just let them die.  Or am I not brining enough ships to the battle?  Assuming I have a Cap ship, how many LF's should I bring with me to take over an Ice planet or Desert planet? 

first thing send your cap first and i recomend targeting the HCs and i dont norrmally use LFs at that point i have LRFs so use those and that should help reduce your casulties

oh forgot to say why you do those things you send your cap first because most ships will attack the cap not your ships (besides the HCs) that is why you hit them first while your cap abroubs the damage while fleet kills remaining forces

Depends on how many and what kind of enemies are in the target world.  Usually the defenders are scattered around, so if you scout and plan ahead of time, you can usually take out some of them quickly before the others make their way from the other side of the gravity well.

A cheap way to claim a terran planet is to kill the siege frigates protecting it quickly (SF's are very weak, so this isn't hard), and then use a colonization cap to take over the planet.  Now, quickly build some defense platforms with your new construction vessels and use them to kill off the remaining defenders.  You can also begin planet upgrades and such at this point.  This strategy works well for Vasari and Advent.  For TEC, a good approach is to just send a Marza in there gung-ho and let it clear out the gravity well.  Good experience, and you don't lose any units.  Wouldn't try this on a small map, though, since your Marza may be needed to stop an enemy rush and having your shields already depleted wouldn't bode well.