At Party, you can guess which tables are the loosest from looking at the average pot size, however this can equally mean that you've got some ultra-aggressive players at the table, which would instead mean that every pot gets raised pre-flop, which is fine if you can handle the swings and play against that kind of player, but probably not ideal for a beginner ABC player.
This is one of the reasons that I haven't played at Party that much, despite it having a reputation for fish - it is missing the key indicator of a good, loose table - the % seeing the flop - from their lobby stats.
Almost every other site has this information, and it's invaluable. If you want to play basically ABC poker (with or without a few enhancements from your own experience), then you ideally want a loose full ring game, and therefore you want to be able to identify those tables quickly and easily, which you can't at Party, but you can at Stars, Pacific, Paradise, SportingOdds,
32red, you name the site apart from Party, really.
Some other things to note. The loosest players tend to be at the lowest stakes for the site. This means on Stars the very loose games are 0.02/0.04. On some others it's 0.50/1.00, because those are the lowest stakes they do. For getting some cheap experience, then, Stars is good, while the 0.50/1.00 tables at other sites may be more profitable for you because they may well be looser.
The looseness of sites will also vary depending on their active promotions, etc. When a site has just launched and people have money won from
freerolls and the like during beta, then they'll be playing very loose because they won't care much about the money. Equally, when a site is doing a lot of advertising in non-poker media (e.g. lads mags or TV or on public transport), then they'll get more non-serious poker players joining up, and those players will tend to more often be the loose-passive type. Sites like SportingOdds will get players who have won money from a bet on the horses or the like, who fancy a 'flutter' on the poker tables, so you may find looser players on those sites often...
Time of day also affects things. If you log on at times when drunk people will be coming home and logging on, then you'll get looser, more aggressive games, while at some hours (e.g. during working hours), you'll get tighter games.
There's a lot more to it than just games getting tighter... there's various things you can look for to find looser games. I've seen an Omaha H/L ring game with 7 players where 96% were seeing the flop at $0.50/1 stakes... (and yes, it was a profitable table
)