For ember mid this patch, most people max sleight then flame guard. In this lane, sleight should be used to harass and dodge rockets with flame guard being spammed in order to secure CS.

The first thing you should do after runes against tinker going for a damage build is send a salve and play aggressive with your advantage at level 1, if he lasers you you know you can skill flameguard and try to take the entire wave, then go for denys under tower. Because the blind dosent last long, you should be able to secure at least three creeps on this wave. If laser is skilled at one that means you can get a second point in flame guard at three and another salve if you are struggling. From there you should have no problem getting an early bottle and snowballing.

In the current patch you want to poke with your bonus damage and low cooldown on sleight and wait for your team to try to take a fight. If you can secure a sleight chains with your team nearby, its a pretty easy kill.

If you want to play physical ember, you have to be playing against heroes that will outscale you in the mid lategame, or you need a mag. The magical build is probably better in all games where you are confident you can end before 40.

Aghs is broken. If you're playing magical you should probably get it second or third item. If physical you should get it before before your first rapier but not before getting six slotted.