For two-footers and in, I make sure to make an agressive stroke and pretty much take the break out of the equation. I line it up with the cup and accelerate through the ball crisply and confidently.
Three-footers are pretty much the same, though I pay a little more respect to the break. Unless it's a really tricky pin location though, I rarely give the hole away completely. I still make sure I make a confident stroke. At worst, I'll lip it out -- but more often than not, it goes in.
Being tentative about any aspect of the putt inevitably leads to a decelerating stroke, which (in my case) leads to either my hands becoming too active through impact to compensate, or a weak push to the right that won't get the job done.
Just spend time on the practice green. Hammer putt after putt into the back of the cup. Do the same for every hole location on the practice green.