Besides a turkey baster, which i think is the best. Stick it in, squeeze it, release and it sucks it in the tube. I dont have one so I have just poured a little bit into a cup. Not sure if that is the best way but its the only way I have.
Don't pour! It'll aerate the beer, as well as stir up the sediment. Either use a wine thief, which is designed for that purpose, a siphon, or a turkey baster! As long as the tool is sanitized, those all work fine.
I use a wine thief. It's so easy, and they cost $8 at my LHBS. I transfer it into a cylinder designed for measuring gravity. I take out about 6 oz per test, and I get to taste the work in progress.