Make sure you know about "Wagering Requirements"!
Whenever you take up any online casino bonus offer, you subject yourself to what is called "wagering requirements", meaning you need to wager the money, bonus plus deposit, a certain number of times in order in order to withdraw.
Say you deposit $30 and get a $30 slots bonus and it includes a wagering requirement of 25x. This means you have to wager $1500 (30+30 = 60 x 25 = 1500) in order to be allowed to withdraw. It may seem like a large amount, however it is not insurmountable.
The key or tip to meeting the wagering requirements is to stay away from high variance slots such as progressives, because these will eat your bankroll if you do not receive the big hit. Try playing games that pay often even if its little amounts, such as 1 line slots with cherries. The goal is to play as long as possible, as this raises the possibility of getting that bigger hit that will increase your bankroll.
Of course, it is slots your playing, and that with there vary nature can be a volatile game, but by attempting to keep alive provides you with the best chance for beating the house when playing with online casino bonuses.