IMO, try to avoid too much of the open hammer pluck at first. It was one of the first slap 'tricks' I learned. I broke myself of it when I realized that I needed to become
way more selective with where to use it. Sometimes a G, D, A, E, etc. is not the right note for the job and I was defaulting to them to be able to perform the OHP. It was really limiting my sound.
Also, try not to anchor yourself to the root-octave relationship...experiment reaching down for the 7th and not always up for it. Play 9ths and 11ths.
Go for an ostinato groove that YOU enjoy and vamp it, changing little things here and there. Realize when you make a timing or economy-of-motion mistake, analyze it, move on. Sometimes you should just play through them, consider it an honest mistake.
Don't get stiff or over-exert your strength. Keep oxygen flowing to your body, and hold your mouth a certain way.
(j/k)
My favorite advice, from Victor Wooten, is to practice non-funk lines in slap too. It keeps you from limiting yourself.
