Need to get better at slapping...

Use your right hand to ute the lower strings.
Ex. If you slapping the A string, mute the E with your hand.

 

Strap your bass higher so that your thumb is more or less parallel with the strings.

 

+1 That would be my advice. Of course, there are other ways to do it. Find the way that works the best for you.

Peace,
Joe

 

I wear my bass pretty darn high to get my thumb to match up correctly with the strings. I usually mute with an unused left hand finger and let my right hand do the audible work. It takes work to be consistent in hitting the string of choice and none others all the time, but anyone can learn to do it if they are patient with themselves.

 

can youy do a good hitch-hickers thumb? thats what i do, and have no problems. i can hang my bass super low for slap cause i have a great hitchhickers thumb

 

wear it around you house, and slap the lowest string over and over again, until you get it.

 

yeah i try and wear my bass high so my thumb is parallel to the string... but when i first started slapping and i would hit every single string on the bass when i tried to slap I would only fret using my middle ring and pinky finger and lay my index finger flat to mute all the other strings... of course thats not the best way to do it but until you can slap only one string at a time it works well.

 

The further I progress in slapping I find that my thumb is becoming more parallel to the string on the strike.

My accuracy is way better this way, as I'm less likely to make contact with the other strings. My hand seems to be in a much more natural position for the pop, plus upstrokes from the thumb are physically much easier and more relaxed feeling.