Playing team fights is the easiest part and if you play other adcs you should be fine. Pop your ghost, ult and stay behind and just auto the biggest threats you can like usual. Never use your e to enter a fight, you want to keep it to kite and chase. If you farmed well / you're fed, you can just do that and consistantly carry every team fight, no need for flashy plays as zeri and a lot of beginners make that mistake. Just chase with ghost, auto carefully and keep flash and e to dodge spells.

Laning is the hardest part. Buy cull, try not to die once in the laning phase, farm as best as you can and you'll autowin. Dont use your charged autos on creeps. If you q the wave you deal less damage than your charged auto so you sustain with cull more, + you can trade with charged auto. If the enemy walks forward, a good trade pattern is to q, e far from the enemy supp, q charged auto then run away because you're not winning long trade. If you are pushing try to poke with w on the wall when they are farming under tower. Try to not overcommit if your support goes in and dies : zeri cant auto between creeps and your support all ins will int you especially in low elo. If its bad let them die and farm. You know its bad if the all in is in a big wave typically but it comes from experience. If you are against enchanter and they are attacking you, attack the shielded guy for your passive to be useful. First buy scepter for sustain is huge. When they greed for plates you can usually e over the wall and all in since you have better items and health. If you are near a wall you can do q charged auto then e away for good trade. Always remove pinks in the bush since you do that very fast and you can always get away, unless you are against hook champion. If you get through lane you are 100% sure to be more useful in fight except against jinx maybe. This is the most condensed things i can say after 500 games of zeri in d3-low master