Well don't go crazy with too many, but I always like to have more than one thing to work on. I get a little burned out on one, but I still want to practice so I move on to my 2nd or 3rd sleight I'm working on. I usually don't go more than 3 and the 3rd one gets rather little practice time. Find a trick that uses 2 sleights if you like, and practice them. Have a third slight you are working on for when you need a break from that. It probably depends on your personality, but this is what works for me.