The size of any bet you make should in most cases be in relation to the pot.
The amount you bet into the pot will determine what pot odds
your opponents are getting, and so they will either be making a call with the correct odds, or making a call with the incorrect odds. Every time our opponent makes a call with the incorrect odds, we are making a profit as they are making a fundamental mistake.
Sometimes you can also be creative in bet sizing depending on the opponents taking into consideration stack size and position. For instance if you are against a good player say in a cash game then you can bet a standard amount of 70% pot post flop but similarly if you are against a calling station who has tendencies to call big bets we want to maximize this by overbetting the pot that is betting more than the size of the pot mostly on later streets.
Standard pre flop bet sizing is a raise of 3bb + 1bb for every limper.
For tournaments your bet sizing can be a bit different to cash game as i don't like betting 70% pot everytime in a tournament structure.
In a tournament you can make a standard bet ranging from 30% to 35% on the flop. On the turn you can make it a bit bigger betting close to 50% the pot. Then on the river you can bet close to 70% pot. This is not standard and everyone has their own preferences and so make adjustments accordingly.