Rakan has a reasonably poor first clear admittedly, you will have to settle for a 3 camp clear where you're taking Blue, Gromp, then Red or vice versa dependng on the side you start, after this and you using your refills you'll be left with about a 1/3 of health and no smite for scuttle but you'll be done around the 3 minute mark to which you wait, W then take scuttle and return to farming or maybe go opposite river to take the other scuttle. I like to farm to the point where im about level 4 and have enough for Hextech Alternator or Blasting wand for first back.

AP Rakan is one of the safest gankers in the game, doing a lot of damage with his W Q Auto + Electrocute combo but also immobilizing them for long enough to guarantee a kill for your laner, but if needed when you encounter a laner who is oblivious to your gank on the enemy you can E out to them after the trade for a lot of poke, people will not expect your damage and might not respect you walking up for the W. Now Mid to Late game your job is to melt the backline, getting in there with your combo, CCing the whole team with your R and getting out with E, you'll do an incredible amount of damage plus CC that it'll be too overwhelming for the enemy team.