i noticed that my handlebars wobbles a bit when running at high speed...

what are the causes of wobbles?
how to fix it?
preventive measures?

TIA :)

Try to have your rims balanced. Autoplus at EDSA does this type of service. Check your front tyre for pressure. Look for un-even tread wear. Have your bearings checked. If all else fails get a new bike:f

Also try installing a Steering Damper ;)

I do not know what kind of bike you have. But try the things mentioned below. Tire wear, tire pressure, tire balanced, replace leaking fork seals and put new oil in fork tubes.
If it still has a wobble try putting a front fork brace on the bike. A lot of times the forks will flex unevenly causing a wobble. I hope this helps, good luck.