When I log onto Empire, I join the first 2 full tables I can get on. I run Poker Tracker and after a while I can see the table average VP$IP. If it drops below 20, I tend to move on to a different table unless I have been making decent money there. If there are at least 3 people with VP$IP over 40, I will stay on when table average is staill low. This is not very common but sometimes it's a bunch of fish and some tight passives. This is actually optimal for me. I can take down some smaller pots from the tight players while waiting for a good hand vs. the loose players.

What do you multi-tablers do as far as table selection?

I plan to move up to 3 tables soon if I keep doing well at two. I pay attention to whatever table has raises to see what people are raising with and how they act. This may be more difficult at 3 tables, but I'll just play a little tighter and base more decisions on just the cards.