1st Ability - Bouncing Bubble (Moonstrike)(1)
is the most important skill with your ultimate ability, I'll tell you why in a second, first of all you need your 1 to help eliminate minions off the lane and help your ADC/Carry maintain a consistent flow of EXP and GOLD, this also goes if you're playing as a solo laner.
Second, your 1 is the most used ability in your ultimate, you just trap someone in your waves and start spamming your 1 until you hopefully kill him or have a team mate help you, you slow you stun and slow and stun again dealing a lot of damage, it is really useful in team fights and focusing targets that need to be eliminated.
2nd Ability - Mending Waters
Use you're 2 wisely because this literally wins team fights, if you have a CARRY or A JUNGLER that needs to be healed instantly he will be also the ability bounces of teammates giving them Armor and Health, buying a lotus crown will help you even more at giving more protections to your teammates, DO NOT use your 2 for dealing damage, because its so precious and takes a lot of your OMI Charges, if you wanna deal damage with it FINE but ONLY if you need to.
3rd Ability - Riptide
Your 3 is mostly used to escape fights and get out of situations or chasing an enemy or even blocking them from running and make them just bounce back to you. also uses a lot of your OMI Charges so be careful when and where to use this ability
Ultimate - River's Rebuke
Your ultimate is basically two walls or two waves that are literal walls like the walls in the game itself, you cant get through them unless you have Ghost Active, but the good thing about this is that you can trap a lot of GODS inside and just let your team do the rest, all what you need to is spam your 1 because inside your ultimate the OMI charges recharge faster giving you more room to do some crowd controlling there. you can also use your ultimate to help a teammate escape a fight and trust me protecting your teammates will be worth in later stages of the game because you cannot carry the game solo.