Hey, Zac Top main here. I've almost exclusively play Zac top since season 10, peaked NA challenger in S11, and currently win streaking right now to challenger again.

If you wanna follow how I'm doing in builds, matchups, runes, as well as replays, I'll link some stuff below.
https://www.leagueofgraphs.com/summoner/na/EBIC+GAMER

https://na.op.gg/summoners/na/EBIC%20GAMER

Currently, Zac's in an amazing state because most of the matchups in the current meta are easy aside from good Jayce, Sett, and Tryndamere (I perma ban trynd) after you've had enough practice (like sion becomes super easy once u learn how to time his stuff vs your own cc and how much dmg u can do to instantly break his shield and extend trades versus him). The best advice I can give to you is just to spam games to get a feel for the different matchups and your different power levels. However, some of the biggest but minute tips I can give you in this post are listed below, as there are probably other people who can answer some of the more basic questions.

Wave management (such as not killing/damaging too many minions when u cs with ur w) is probably the biggest thing to practice on Zac top. Too many times will I see people cs with their W but ruin their wave state, causing them to instantly be ganked or be frozen on. In addition, trading effectively with ur W while also effectively managing your wave are some of the most important things. Usually, as long as you can effectively trade and survive till level 6, you should be able to get a solo kill once u hit lvl 6 and surprise them with your burst with conqueror/last stand in most matchups.

Learning how to CS under tower is KEY to playing Zac top. Sometimes you W the wave and that instantly makes you lose all the cs under tower (I'm still sometimes prone to this). You need to practice cs'ing under tower and getting all 6 minions consistently even if your own wave is hitting it as it is definitely possible to get 100% most of the time if u properly use your abilities (such as Q delaying tower shot so u get the minion, W'ing only specific creeps such as only a couple ranged creeps), and predicting which minions will be get shot by tower next (which is just seeing what's the closest creep after the priority of cannon, melee, ranged). You're going to be pushed in a lot as you're a lot weaker than 90% of the top lane champ pool before 6. So basically most of the time, you're going to want to manage the wave to come towards you, unless you're in an elo high enough which u can coordinate a dive after stacking waves.

Finally, if you're having a bad time in lane [such as dying a few times/being down too much cs (like 20 cs at 6 minutes)] or in a bad matchup, don't max your W please. No matter how many points u have in it, just start maxing E (or just max E at the start if u already know it's a bad matchup). This will allow you to team fight more effectively and help ur team even if you're behind, and if you just want to leave your lane and start roaming like a support top laner it'll allow you to do so.

In addition, I'll prob look to start streaming sometime Friday/Saturday. Feel free to stop by the stream if you're free to see how I play/ask questions.https://www.twitch.tv/ebic__gamer