I always go BL first but some go SS. But i think BL is more important cus u can get 1st blood easier and lane longer.

In a fight i do MS first to decrease there hits and slow them if they try to run immediatly, after i attack maybe throw in a SS let my crits do most of my damage.Then when they run ill SS them and or exhaust, then by now MS should be ready and i slow em down SS again and they should either be dead or close. =)

Make sure to always last hit minions for it gives u stacks on BL and u can heal from it. Also when u want to gank some one u want BL stacked or at least till ur higher level. As for when ur higher u can stack it just from attacking them.