You're pretty new to the industry I'm guessing. Estimation is one of the hardest things a developer can be asked to do, and the only technique that will consistently work is getting experience so that you have similar tasks to compare the one you're estimating to.

In the meantime, try to break things down if you can't even start on an estimate - what are the steps involved in making Task X happen? Keep breaking those tasks down until you get to something you can estimate. That's what the estimation time you ask for is used for.