Make sure you avoid climb milling, especially given the inherent lack of rigidity in your set up. Think of climb milling as feeding the work piece into the cutter such that the teeth are climbing up on top of the work piece. Make sure you do conventional milling- milling so the cutter is scooping up the material. I'm sure that explanation was confusing, not really sure how else to word it.
AvE on YouTube had a series if videos where
He converted a super cheap Home Depot drill press into a relatively effective mill with a decent XY table. If I can find the link, I'll post it here.
ETA: Here's the link to the video.
-Tanner