I usually play three 6 max tables at once, but I make sure to close down the ones with particularly tricky players and find an easier venue. It's not that I can't win in those games, but it robs too much of my concentration from the other tables.

I also use some tools, like Pokertracker and Playerview to make reads a little easier.

Finally, when in doubt, sit out. If you don't like your play, simplify and focus on one game until you're comfortable in it. Then add the next table.