in order to get a solid spin you need two things power and technique.
#1 Start with a good tight bind. Whether you are throwing a front spin ( sleeper) or a side spin ( breakaway) start with a really srong throw. you can never throw too hard.
#2 During front spin: after the yo leaves your hand but before it gets to the end of the string, pull up on the string, hard! if you did it right you will notice the difference. another way to do this is grab an offstring yoyo and practice the power throw ( 4a equivalent to the 1a sleeper) when doing this throw with a 1a, throw over your hand but don’t worry about catching it. after the yo is thrown over your nonthrowhand finger just pull your throwhand back. !!! will burn fingers !!!
during the side spin: throw up and out and as your yo is unwinding from the string pull the sring out as you guide it. ( your throwhand should look like its doing the hook whip during your throw) you want to pull the strig out of the yoyo while its in process of the throw but not so much as to pull it off its path !!! I always pinwheel my breakaways. for safety purposes. the yoyo will be less likely to OWN YOUR FACE if you pinwheel. good idea if you are going to be whipping aroud a metal yoyo !!!
Using and pefect these techniques will greatly improve the spin on your yo.