Help with starting out in MP

I would say, first level go AOE, just get your AOE spell and farm creeps.

If you are rook, go hamer slam, kill creeps change lanes always go against the creeps and forget about the enemy DG, at level 3 with hamer slanm and archers theres no other dg that can actually go against you without risking dying.

Since the above part is a little to simplistic and general let me try to re-frase. I belive what you are doing wrong is let others harras you, if someone atacks you fall back to towers and atack them, of course that depends on the map and DG, lets take for example rook since you said you like him and lets take the map prision, now in that map you can really fall back without losing to much ground so what you need to do is just put 2 towers on the 2 lanes and go around hammer slaming, this aplies to any map, yu get exp from the kills of your towers so use that to gain exp by changing lanes and setting towers in any place where creeps should be.

look me up in the chat and we might play a game, im not an expert but i can show you a few things with Rook, TB and Regulus.

Starting out? Depends on what DG I'm playing and what DGs I'm against. 

Every DG can sit around there tower and just leech exp from the creeps. You don't have to actually kill the creeps to get exp. Early on towers do 200 damage a shot, so no one will dare go near them. If the enemy is killing your creeps, just hang around tower, and it'll kill the enemy creeps and you get exp. 

If you're playing as the rook, get the towers, and start raising towers near where the creeps do battle with each other. Then go start capping flags - this gives heaps of xp early game. Harass enemy dg's around the flags and when they farm creeps, but don't die - don't stray too far from your own towers. If an enemy dg comes to attack you, raise a tower then hit him a few times - at level two grab the hammer slam, use that on dg's, don't waste mana casting it at creeps.

I cap flags. Dont waste time, get out there quick (buy your item before choosing your skill and favor item, those 2 can be done while you are moving) and capture a flag. The flag capture and some times one or 2 creep deaths near you is all it takes to hit level 2. Kill the rest of the wave, head to another flag (preferably one in a creep lane).

Thats the tactic, the variable is enemy DG's. Play accordingly. Stay safe, harass when you can. While flags are always worth good experience, once you get to levels 4 and 5, it becomes less important and you can stop grabbing flags for expereince purposes. Which is to say, do your best to keep control of the flags, but no longer take the experience gain into consideration when choosing what to do.

This is the tactic you spoke of, where your oponents are level 4 while you are just coming up to level 2.

Hope it helps!

Chaos

(PS: A little note about Karma. You need to click the little thumbs up button below this post if you want to give it to me. Giving it will cause more people to take my advice seriously. If it helped you, do others the favor and let them know its good advice!)