There are so many suggestions and they're all right in a way... but you have to find your own.
The actual answer is and only ever can be:
Practise
Or you can do what I did - a 21 day challenge. 10 compliment approaches every day for 21 days. By the time I was done with the challenge approaching was becoming mundane, boring and routine.
Which is better than scary, I warrant you'll agree!