You will see a lot of pros working through a routine before they head off.
I like to hit 3 / 4 foot putts from around the hole, work on 7 or 8 balls, and if you miss one start again. Once you are solid from this range you will find it boosts your confidence and you make more of these knee tremblers
If its a longer putt where you realistically aren't going to hole out just try and get it within a dustbin lid of the hole.
For shorter putts: Use a smaller back swing but hit through the ball more with a long follow through. This means the club head will be accelerating through the ball rather than, if like me, you slow the club head down in fear of over hitting th e putt.