In playing live poker, tells are a central part of the game. You want to seek to gain information from the behavior patterns of your opponents, all the while trying to make sure you're not giving any information to them that they can use against you.
In online poker, we don't have the ability to watch our opponents' behavior in the same was as we do at a live game of course. This doesn't mean that we don't have anything to work with though, and by paying attention enough there is still some useful information to be gained.
Let's start with our own play. What we want here is a "poker face" of sorts, which means being aware of the possible perceptions of others when it comes to how we are going to be represented and perceived at the table. There are nuances that others may potentially pick up, such as the time it takes for us to decide to make a move in a hand, and we don't want to give away anything we don't need to. Even at the weaker games where it's unlikely anyone will be looking for tells, this still may have an impact at least subconsciously on our opponents. For instance, if we make a move very quickly, this may add to the perception of opponents that we are strong, whereas if we take our time and seem to be doing a lot of thinking, or holdings will seem more marginal, whether or not our opponents are thinking this through consciously.
The natural way of playing is going to be to act quickly when we're certain, and more deliberately to the extent we aren't. First off, it's usually not a good thing to display strength by acting too quickly, as we don't want to do anything we don't have to which would risk undermining the confidence our opponents may have in their own hands.
Therefore, it is best as a general rule if we take our time a little more and try to develop consistency in the amount of time runs off the clock before we act. Not only will this show deliberation and to some degree uncertainty, it will allow us to have more time when we actually do have to think more, without showing an obvious difference between that and the time we spend when there is little to consider.
Another advantage of this, and not an insignificant one I might add, is during these extra seconds we will have more time to think. It's never good to be too hasty in acting anyway. And we can use this extra time to consider things in a little more detail than perhaps would be natural. As an example, we can replay the action so far and consider what certain players may be holding. Or consider our position more. Or look toward what other players may do after us. And so on. Extra time to think is never a bad thing, and if used wisely, it can help prevent mistakes. And every mistake prevented adds up to more money in our pockets.
From time to time, it may also benefit us to take even more time, when we're particularly strong and fear opponents may fold. This will offset the times we do need more time, whereas in the first case we have a very strong hand and an almost certain winner, and in this case we have a hand we're genuinely not sure about. We don't want to do anything to help our opponents read us, and the more we keep them guessing, the better we'll do.
Now, our opponents probably won't be using such tactics, and we of course will be looking to see what their actions may reveal to us. We're going to assume their actions flow naturally, in other words, their speed of decision is going to be in accordance with their relative confidence in their hand. If a player acts in a way that he may be trying to deceive us, we can take that into account later. Without any such evidence though, it's better just to assume they are playing it straight.
Of course, you need to keep in mind the general skill level of the opponents when doing this, to use as a reference. For example, a player may think it is always wise to call bets, or even to bet, with second or third pair. That being the case, he may do so very quickly. And some players may play nothing but quickly. When players don't though, we may look to put them on a weaker hand than we would otherwise.
Another key element in the play of our opponents is checking and calling. Opponents often aren't afraid to bet, and when they go into check and call mode it often means they don't have a strong hand at all, or are on a draw. There's 2 elements we want to be aware of here. First, we probably have these people beat now, unless we're on a draw ourselves. Secondly, we want to be more careful when cards that may complete draws hit. Third, we want to pay even closer attention to variations in their betting pattern. If they were checking and calling in previous rounds, and betting in this one, it is cause for concern.
There are all sorts of other things you can pick up while watching opponents, including such things as their handles, their avatar if the site allows it, their chatting, and so on. While these things can occasionally be helpful somewhat, it's best to focus more on their play and not worry too much about these other things, unless it's something obvious like the guy is on tilt or he is displaying a lack of understanding. An example is people who get angry on the chat when they suffer a drawout, or players who show their stupidity on it.
A good exercise, and one that is worth spending time on, is simply watching a game and trying to decide who among the players at the table has the better hand simply by watching their actions. It's important to do this while not playing at the table, so you can be free of distractions. With a little practice you'll probably surprise yourself at how many times your predictions will be accurate. This skill will of course come in very handy when you go back to participating.
To sum up, you don't want to give away your actions any more than you need to at the table, in spite of what you may think of the sophistication of the competition. Consistency of action is the key here. With your opponents, we'll be looking for inconsistencies to indicate weakness, as well as anything else useful we can pick up while watching. Doing this properly will further your advantage at the table, and you can't have too much of an advantage, just as you can't take too much of their money.