When I know I want to dedicated myself to a long session, I open up at least 5-10 tables for at least 10 observed hands. I'm looking for the quintessential LPP table: highest VPIP, lowest PFR, lowest TA. If there are two similar I use the higher pot size as a tie breaker. Also, if there are more than 1-2 people in line in front of me I choose another table - chances are that there are sharks waiting in front of me. Once I start playing I keep at least 2-3 other tables open in case the one I'm at gets too short-handed or too taggy.