Tips to Use Riki (Dota2)

• It is usually recommended to get Permanent Invisibility as soon as possible.

• Casting Smoke Screen after using Blink Strike will stop enemies from escaping or fighting back after a sudden attack.

• Although chasing enemies might be useful, it is recommended not to be too reckless. If Riki is revealed, he can go down very quickly.

• Blink Strike can target allies and enemies. Jumping to a friendly unit can be useful in case Rikimaru needs to escape.

• Using items no longer drops Riki's invisibility. In that sense Dagon can be purchased for hilarious results.

• Although it is not mentioned, a Heart of Tarrasque can be a good item for Riki; his Permanent Invisibility allows him to slip away and let the passive regenerate him without fear of interruption. 

source: http://dota2.gamepedia.com/Riki