The early action buttons most commonly used are Fold, Check/Fold, Raise, and Raise Any. It will be clear when an opponent constantly used the early action buttons. It will also be clear when he breaks that pattern and gives more consideration to a hand. That could be usefull information, but at the same time, it could also be indicative that the player was busy doing something else - on the phone, checking mail etc. Do pay attention to the timing of an opponents bet for online tells that you can use to your advantage.

Adjustment: When an opponent stops using early action buttons and gives more thought - often it is because he has a strong hand. When in doubt, fold hands in this situation.