A main consequence in strategy of the virtual nature of online poker is that players cannot see each other. That means that there are no physical interactions between players, and that there could be no observable physical behaviors. Thus, tells in online poker are almost obsolete.
And because there are no physical tells in online poker, a few poker plays become more potent. Deceptive plays like bluffing and slow playing become easier to pull off, since one does not need an emotionless poker face to prevent others from seeing your schemes.
The strength of each player's hands becomes more difficult to read too. This is because the behavioral quirks of players cannot be seen. Thus, traditional tells like shaking hands when a player holds exciting cards or a sweaty forehead when they are trying to pull off a difficult play could not be relied upon.
This is both a good thing and a bad thing. A bad thing, because players cannot lure other players by acting out false tells, and cannot easily profile other players by relying on physical tells. A good thing, because poker is reduced to its most basic and important features, which means that the game becomes more pure.
There are still tells in online poker, which are not based on physical behavior anymore, but on game behavior. This means that the tendencies in betting, fold-and-flop percentages, and actions based on pot odds are the ones that you should look out for.
Yes, this does mean that you need a good understanding of poker mathematics. If you think that it is really burdensome to learn, maybe you need to reconsider. Once you become proficient in computing probabilities and using them to predict a player's action, you can easily decide on which plays you will execute.
What's more, a good grasp of poker mathematics will still be useful even outside online poker. You may have the convenience of a calculator at your side and the automated display of pot odds in the interface of the online poker, but you will eventually get used to it and could be able to 'feel' for the probabilities.
Keep in mind that since tells in online poker are more pure, it also means that deception is a really risky but potent task. Thus, bluffing and slow playing needs a good build-up to trap players.
Remember that tells in online poker are based on game behavior: betting tendencies, fold-and-flop percentages, and pot odds reactions. With a good grasp of poker mathematics, you will be able to keep on reading your opponent's tells, and lure them into your fake one.