You may insert a finger in your vagina and contract the pelvic floor muscles till the finger experiences squeezing pressure.
Repeat the squeezing of finger several times by keeping the finger inside vagina
Remove the finger and repeat the exercise several times.
Once you get control on these pelvic floor muscles you may do the squeezing exercise without inserting your finger in vagina. For better strength of muscles, do the squeezing at least 20 times and as much faster as you can. You may do this exercise anywhere, like while waiting for the train, sitting in the car or while listening to music.
When you get better control on squeezing of vaginal muscles, you will start experiencing more pleasure while masturbating.
With experience you will be able to grip your partner’s penis more pleasurably for mutually enjoyable sexual pleasure.