How can I avoid bike thefts? There are several points you can do:

• Always use good bike locks when locking it. For instance, follow the advices here and here
  

• Lock your bike to solid, robust objects.

• Lock your bike in place of passages. This way someone can see a theft and call the police or at least threaten him to do it.

• If you can, select strategist places to lock your bicycle near such as police stations.

• Do not let your bike rest at night under the stars, better allow it to do it indoor.

• Perhaps use a psychological trick like this one
  

• Never buy a bicycle without receipt. If you do not follow this advice, you are probably supporting bike thieves and the black market.

• If you can, do not legally buy a colorful bike since this fact attract people eyes including the thieves ones.

• Decorate your bike with an anti theft sticker. Not sure if this would stop a theft, but at least it can make you laugh: