Watch out for the following:
All of the following things are illogical, and should not be used to cloud your judgement.
Looking at the previous results as a source of what is likely to happen
Previous results (spins, cards, wins or losses etc.) have no bearing on th next event. The spin is no more likely to be black if the last 5 have been red. Similarly, there is no such things as "hot" numbers etc.
The casino lets you win early then starts to make you lose
Everything is random, online casinos are not fixed. You are just as likely to lose on hand 1 as on hand 10. It just feels like you often get off to a good start then fail, because if you fail straight away you dont have a chance to recover.
Betting to get back to where you were
There will always be wins and losses and you will never know what your highest point will be. In the long run however your bank will go down, so if you start to lose a few, pick a get out point, dont try to get back to where you once were. Always treat your bank as 2 losses lower than it says it is, then you wont feel like you ever had that money.
Playing games you don't understand
If you know the rules and the best strategy you have a far better chance than if you dont. Imaghine someone who doesn't understand blackjack, they are far more likely to lose if they start splitting tens and sticking on 7 than if they play to the optimal strategy. If you wouldn't play blackjack without understanding the best strategy then dont play the new games such as "Deal or no deal" unless you are sure you understand them too. .
Practice like you would play
Most games allow you a free version to play without risking any money. People often are a lot braver when it isn't real money, and consequently they appear to win much more money. Dont be fooled by this. Unless you are going to be that brave in real play as well then it isn't a fair practice.