Overview
You shouldn't engage in early without teammate before getting your first item. If they freeze the lane don't be greedy. Freeze the lane as much as possible and farm first.
Strengths
He can change any fight situation if you can position yourself. He can mostly burst mage, mm and squishy with 1or2 skills.
Weaknesses
He lacks mobility so using flicker is best choice. He also lacks range so it is risky to attack long ranged opponent. Without proper farm he is extremely weak. Pushing turret is hard with him.
Burst Critical
You can replace boots with Sea Halberd and the Malefic Roar to Malefic gun if you are ***********. This build is recommended if the opponent has squishy heroes.
Burst
Change the boots with Hunter Strike if you lack damage in the late games if needed. Use this build if opponent have 2 or more tanky heros.
Critical
You can change the Fatal to Rupture and the Quantum Charge to Impure Rage depending on opponent line up. Use Impure Rage and Rapture if the opponent are tanky.
Battle Spell
Flicker is the most recommended but you can change it to purify if the opponent has a lot of crowd control. Aegis is also a choice but is rarely useful.
Macro
Avoid early battles. Farm as much as possible and take the gold crab as many as possible. Always stay behind tank or fighter. Don't engage fight without teammate if you are loosing or the opponent are over farmed. Clint can usually dominate after his 3rd or the 4th item so prioritize farming.
Best With Tigreal
They match very good in team fights. With Tigreal's Crowd Control Clint can stay behind and burst the enemy quickly and safely
Watch Out For Miya
She can burst him down after using her ultimate but she can be counted with Wind of Nature.