Poker involves all the playing styles possible. Anyone that doesn't want to play against a particular style is limiting their game and will hamper their development. (Granted .. sometimes it's preferable to play at softer tables ... but do this always and you'll become soft)
Anyway ... online there's not much in the way of tells
, all just stats and numbers. But! hover over your opponents who are in blind(s)\button and you'll see my favorite online tell .. "Nationality: Russian".
Our Russian friends will put you to the test so make sure you're playing comfortably within your BR.