okay look fam you got three options pretty much:

3-camp clear path to mid or transition into 6-camp clear
Red buff -> Krugs (smite) -> Raptors -> Gank / Transition
Blue buff -> Gromp (smite) -> Wolves -> Gank / Transition

6-camp clear
Red buff -> Krugs (smite) -> Raptors -> Wolves -> Blue (smite) -> Gromp
Blue buff -> Gromp (smite) -> Wolves -> Raptors -> Red (smite) -> Krugs

3-camp clear path to bot or top
Red buff -> Raptors (smite) -> Krugs -> Gank
Blue buff -> Wolves (smite) -> Gromp -> Gank

when deciding on what path to take, take into consideration
lane matchups: if your laner wins lane probably gank them
enemy picks: if they have a weak early game BULLY THE SH*T OUT OF THEM
lane occurences: allied laner shoves lane? probably don't gank that maybe a bit risky. enemy jg ganks someone and you're nearby? SMACK EM!

Q(in w) -> W -> AA -> Q -> AA -> E -> AA = YOUR BREAD AND BUTTER

You can modify this combo as much as you like, to include stuff like Prowler's Claw or maybe just knockup with W early because you don't have the time to Q(w). ALways E with max fury though because it deals double and as true damage.

Rek'sai has an incredibly strong early game. You should make as many plays as possible. Use your tunnels and fast clear to get camps quickly and efficiently. Gank using tunnels, flash to secure kills. Its alright if you die a couple times, as long as you get value out of it eventually. You can also invade pretty easily, keeping track of the enemy jgler's position (if ahead, just chomp; if behind, avoid)

Ideally you'll get a Serrated Dirk and Boots on your first back after a kill or two. Getting the Herald quickly -> big value because Rek'Sai needs to plating gold and map pressure to snowball the game.

In the mid-late game you'll want to look for picks without too much risk. Target squishies and peel for your own squishies.