First things first. How do you play the game?
The basics covered in the tutorial go over-
A:jump.
When jumping you have acesss(sometimes) to an entirely different set of moves. Some have double jumps, air attacks, air hold attacks, and air dashes. Others just have a simple air+jump attack. It depends on the hero you're using and it's best to learn and understand their skill set before going into the game.
S:Blocking.
This is way more important than the tutorial shows it to be. Blocking can be the difference between not getting hit, and being stun locked into a 20 hit combo.There is also on some heros an ability to counter attack. It's important that on certain heros such as D'Artagnan, to time the counter attack right. Or else you're just going to jump out of a block, and get hit in the face.
D:Attack.
This varies so much for heros it's not even funny. So i'm going to break this into 3 sections.

Basic attack-
Basic attacks are just tapping the d key. It's best if you try to get your opponet to be hit with your basic attack as many tiems as possible without them hitting the floor. Since off the floor they get a second of invinciblity that they cant be damaged in. However, if you have a ground hit(hitting someone on the ground with an attack) it can be worth it to quickly knock them out and then try to bounce them.

Half holds-
Holding the attack key for around 1/4s-1/2s will make it a half hold. This allows for certain heros to use other moves. This is used for certain combos chains. They tend to be half stuns, knockups, or ground hits.

Full hold-
These tend to be either charge attacks such as deathknight and D'Artagnan, or anything from ranged to stuns.These are important for many combos, and you'll have to learn them for each hero.

Switch combo-
This is a bit out of my experience. I have slight knowledge of switch combos with hook and necro. But outside of that it's really top level. If you want to get into, i'd reccomend watching no cash and experimenting in lobbies.

Well now that you've learned and practiced the game mechanics, lets look at where it throws us.
You're going to start off with a perm hero scroll to select any hero. I'd reccomend waiting on this till you learn what playstyle you want. You also start off with a shadow assasain.

Shadow assasain is a very basic hero. He can be annoying at lower ranks, and hard to beat if you're not careful. His main combo goes as-
Dash attack/Jump dash attack > Hold D(poison)
It's a two step combo that is deadly to new players. I would reccomend learning heros who can easily dodge his attack, or ensure that they are not knocked down by his attack, such as the dragon rider, iron knight, or any of their gear.

As for early levels, I'd reccomend trying out some pve(with a group) to get fast levels. PvP will be a bit hard till you learn a bit more of your skills. Generally TDM,power, and prisoner will have heros who will manage to edge you(knock you off an edge) or spammers. Another great resource you can use is going to be the 1v1 lobbies. This is set up so that one champion(winner) fights each challanger (losers/new join) on a 1v1 fight. I find this to be a true skill match when it comes to mastering a hero. I wouldn't reccomend it if you have a timed hero, since your hero times tick down even while in the lobby.

Grinding
The two best ways to grind for xp is going to be 1vAll pvp(you as the 1), and farming powerstone. When farming powerstone, be sure not to be a complete idiot. Don't fight other players unless people want to fight, don't hit the powerstone unless there is an agreement on who's going to win or when to hit the powerstone, and just don't be an idiot. Or else you'll get kicked.

Faction/ranked match.
I wouldn't reccomend this till you get up to 2nd lt.
It's an amazingly fun gamemode, and you get decent xp from it, though you'll find a lot better opponets there then you would otherwise. You also might find people doing switch combos and get owned. Or you'll find a match that is a 8v1/8v2. This is set up so that 4-6 people fight the 1-2 players, and just spam, stun, and slow them as much as they can. Then you have a finisher hero such as ragna, d'artanian, or any fast hitting hero(flash gear works as well). It's annoying, and it works the majority of the time.

Perm heros
Perm heroes are great. These can be gotten a number of ways. 10,000 hero cards being used to craft a hero. Random from a beginner(least likely), hero scroll(2nd least), lucky(good chance), or perm hero scroll(100% chance).

Free Premium items
These can be gotten from events and quests throughout the year. I also HIGHLY reccomend that you go the to forums(z8games.com) and look up the current events. There is almost always an event going on after every update. This can get you things like free zp, free heros, gear, and setup items. It can be anything from a speedrun, to a item contest, to a screenshot contest. Just be sure to make a post on the event during the scheduled days.

So you've been playing for a while, or just read the rest of the guide. This is where you get to learn all the heros that you've been wanting to. This will go over good FREE combo heros, that will get you high on the ladder matches.

I might be adding seperate guides to each of these heros since there is quite a lot of depth to them.
Heros to learn:
These are just a few heros in my honest opinion, that can do so much even though they are free.
Iljimae-While I don't like this hero, he is one of the best. His fast paced teleports and combos allows for him to move and attack at his own freewill.
D'Artagnan-I'll be honest. I have an obsession with this hero. His helm is one of the best in the game since it lets you recover mid air after being attacked. This lets you own heros that are comboing you, or stunlocking you. And allows for you to dodge any skill that knocks you up in the air.

Puppeteer-This guy has the ability to bounce you in the air for eternity. His puppets will be the most annoying thing to deal with if the enemy cant kill them immediatly. Nice hero to learn, but he's honestly one of the hardest(imo).

V-mech-Another great hero. Has good mobility, defense, and a massive attack with his skills. A nice all around hero that can do allright in many feilds But not the best.

Kage ninja- Doesn't have as much depth as the above, but his counter attack is quite nice. Adding a little extra gear to this guy also does wonders. One of my personal favourites, and i'd reccomend at least trying him so you can understand how he works.

Card magician- While I left this out before, I feel that this is another great hero to learn. If you can time his card throws and his jump attack, he is deadly to almost every hero.

Also, if you can get a premium hero, stay away from Sol. While he may look cool, wait for his next reform before buying him. He's currently underpowered and nearly useless for his cost.

Ranked/ladder-
I prefer ladder 1v1 matches over anything else. You get to fight pretty decent people and learn their strats. This should also be the time you're going to want to learn a few switch combos. Even if it's minor. Learn the basics of Skill combos, and early switches like knockdown+hook bomb.

Feel free to leave some advice down below if I misspelled, misinformed, or made a mistake.
I'll also be updating this in the future with more guides for each hero, and possible some youtube examples.

As for now, have fun stunlocking.