When playing online poker the information you get about other players’ hands is derived by observing the timing/speed with which each player makes a decision.
When you are playing you can usually either pre select an action within the poker software or you can click on your next move manually. Sometimes you can glean information by observing the way in which the software reacts based on what your opponent has done.
All of these suggestions are pure generalisations and you should watch out for clever players deliberately using tactics to disguise the strength / weakness of their hands.
Delays followed by a bet can indicate that an opponent has a strong hand
The delays are often used by players in an attempt to trick others into thinking that they have a weak hand. The apparent hesitancy is designed to make others call.
Delays followed by a check can indicate that an opponent has a weak hand
A player who is planning a check raise is likely to check more quickly.
Automatic bets or raises on the turn or river
This is likely to mean that the player has a strong hand as he/she has simply set the software to bet/raise/automatic checks on the turn, flop or river. This can usually be taken as an indication of weakness as the player is hoping to see more cards for nothing. Many people will use the check/fold auto button when planning to fold in the face of any bet.
You can ensure that you do not give opponents any ideas about your own hands by randomising the time it takes for you to make your selections. For example you could wait 2 seconds before checking / raising / folding when the previous card dealt was odd and wait 5 seconds when the last card was even.