What are your general "rules of thumb" when looking for a good "soft" game?

Hmmm, different answers for different games / styles / individuals... my favourite type of game has players who are both loose and passive, they are the easiest to read (will fold bad hands, call with weak hands and only ever bet when strong) and the most likely to pay you off when you hit a monster.

For those players with a loose / aggressive style the most profitable games are probably those with weak-tight players.

tips on playing poker very well?

Sure, bankroll management, site / table selection and (most importantly) good betting + bet sizing strategy (habitual 'callers' are not long term winners in poker... aggression = $$$).

Cheers, Mark