Can anyone give me any tips to snap start yoyo?
The main thing is practice. Mess around with where you put your fingers on the yoyo and find what works best.
Thanks, I guess
When placing my thumb, I like to use the inside of it 
I feel it gives me more grip, hence giving me a better snap start.
I use my thumb and middle finger, lining them up parallel to the ground; then a rotate them counterclockwise 90 degrees or maybe a little more so the thumb is at the bottom of the yoyo, and the middle finger is at the top, then snap clockwise quickly, rotating the wrist a little during the snap. I also found that you have to get a feel for how tightly to grip the yoyo - for me, I try to not squeeze it too hard.
Try only using your fingers to snap start the yo-yo. Like what Apetrunk said, mess around until you can find a good grip. Once you get better, add a little twist of the wrist to give it a faster spin. Hope this helped!
Oh just thought of one more tip that might help: try keeping your throw hand elbow away from your body a few (six maybe) inches to keep your finger(s) and thumb lined up perpendicular to your chest. Otherwise, if you let your elbow rest against your body, you’ll notice that the line between your thumb and finger(s) will be pointing several degrees to the right, so if you try to spin start directly forward, it will end up giving a big wobble.