Well, here's some things you SHOULDN'T do.
Godmode - When you rp, try to not make your rpc do something completely unrealistic (in an Anime sense) to avoid an attack or land one.
Ex.1
*Buttman runs toward Coolguy to punch him in the face.*
*Coolguy increases the gravity in the area to hinder Buttman's movements. Coolguy then sidesteps to knee Buttman in the stomach.*
*Buttman activates his secret technique that makes him immune to knees to the stomach, thus remaining unharmed.*
See what Buttman did there? He was unable to properly escape the attack so he used a cheap way to get out of it.
Autohitting - I see mostly higher ups do this more than anyone on the site. It's never cool to autohit, no matter what rank you are and what rank you are going against. If you believe that certain circumstances prevent your opponent from avoiding an attack, state them. Take Buttman and Coolguy for example, after Buttman launches his attack.
Ex.1 *Coolguy had increased the gravity around him and Buttman. Doing so prevented Buttman from jumping, and since Buttman was running towards Coolguy, all of Buttman's momentum would be going straight foward, preventing him from side stepping. Also, Buttman had very little chakra, so techniques were likely out of the question. Not to mention Buttman was extremely close to Coolguy. Knowing this, Coolguy sidestepped Buttman's punch and countered with a vicious knee aimed at his stomach.*
See? Coolguy's post is basically the same as before, only this time Coolguy explained why Buttman shouldn't be able to dodge the attack.
Metagamming - Basically when your characters has knowledge of something they shouldn't have because they never experienced it. I'll give an example.
Ex.1 *Coolguy summons a large titan, summoning it for the first time against Buttman. The titan is immune to every element but Wind.*
*Buttman sees the titan and begins to charge wind chakra throughout the area. Buttman then unleashes a barrage of Wind jutsu.*
From the example above, this is Buttman's FIRST time encountering the titan, therefore, he should not immediately know that Wind is the only thing that can hurt him. However, there is a correct to do this.
Ex.2 *Coolguy fights Swordman and summons a large titan.*
*Buttman sat in a tree and watched the fight.*
*As the fight dragged on, the titan seemed to be to tough so Swordman uses one of his strongest attacks, a massive wind tornado. The wind tornado connects damaging the titan. Swordman then slashes the titan with more Wind techs, and unlike the other elemental techs he used on the titan, the Wind techs actually hurt it.*
Now, in Ex.2, Buttman WITNESSED the fight and saw for himself that the titan was weak to wind. Therefore, when he fights Coolguy and he summons the titan again, Buttman will know exactly how to beat it.
This is all I can think right now....