Hey Joanne, the best tip I can give is that the speed in which you “hammer” your finger down makes a difference. And it doesn’t take tons of pressure. As an exercise to work with you can try this. Press down the 2nd fret with your middle finger, then pluck that note and hammer down onto the 3rd fret with your index finger. The index finger is usually stronger than our other fingers. Also do this one – press down the 2nd fret with your ring finger, then hammer with your index onto the 4th fret.
You can work your pull off’s right after doing the hammer on. And if you don’t hear 2 notes with one pluck of the string something isn’t right.
To help much more I’d need to see you. You can do it!