Geonosis is a rather large map, with quite a lot of space in it, and therefore your opponents can be scattered around with great distances between them, making it more difficult for you to, for example, throw a grenade into a large group of them and send them flying. However, if you are playing as the CIS (playing as the CIS is the only way this strategy will work), you might have noticed that there is one point where the Republic Clones always assemble in groups - near, or inside, AT-TEs. Now, you may be wondering how, if they are all inside the AT-TE, you are going to get at them.
Firstly, spawn as any droid type at a CIS command post near the Spider Walkers spawn. Hop into a Spider Walker and start making your way towards the AT-TEs, which will be heading towards you. The secondary weapon of a Spider Walker is a laser beam, and this entire strategy revolves around that weapon; aim for the little cannon protruding upwards from the top of the AT-TE, where a Clone is always sitting. Blast him with the laser. After doing this, another Clone will take his place. Keep blasting, sending Clone after Clone hurtling to their doom, and you will get a huge amount of kills and points. Although the laser beams continually impacting with the AT-TE will eventually result in its destruction, don't worry, just wait for another one to appear and you can go off on your killing spree again.
Depending on what settings you have for your hero, Count Dooku may be available to you at some point during your killing spree. It is best not to spawn as him, and stay in the Spider Walker to continue blasting. If you spawn as Dooku, this strategy may not work for you again. However, if you are rather fond of Dooku, there is an alternative strategy which enables you to use him and get a lot of points. Spawn as Dooku and head to the nearest AT-TE. Jump up onto it and start hacking away with your lightsaber. Loads of Clones will take the spot of your previous victim in the seat, and you can throw them off again and again and again. This strategy will also destroy the AT-TE eventually, but don't worry, you won't be destroyed with it.