There are dozens of different opinions on what makes a good roleplayer. However, what constitutes bad roleplaying can usually be summed up with a few core complaints. Here, I've attempted to gather those failings together, and explained why they're bad or offered ways to avoid falling into those traps.
Playing a caricature, not a concept.
There are a few things that canít really be helped when making a character for an RPG. Fighters fight, paladins crusade against evil, clerics worship their god. However, that should not be the end-all-be-all of your character. How and why does your character do what he or she does? How are these things likely to affect her in the future? Until you can answer these questions, donít even pick up a character sheet.
Thinking your numbers are your character.
This is closely related to #1, but separate enough to have its own listing. So you have a class, you have stats, you have skills, thatís all well and good. Now put those numbers away, theyíre arbitrary. Why does your wizard have maximum starting intelligence? What kind of training did your martial artist go through to ensure he has the skills he has? Your character sheet may be the framework that your build your character from, but remember that itís exactly that: a framework. In the end, your character sheet is really only needed for game mechanics.
For those who arenít aware, min-maxing is the method of trying to extract as much power from your character as possible by severely hampering unimportant stats. For example, the base stats for a min-maxed Dungeons and Dragons fighter might look something like 18 STR, 16 DEX, 18 CON, 4 INT, 10 WIS, 3 CHA. Unless youíre willing to roleplay a barely functional, completely unpersonable character, the gamemaster would be well within his rights to reject these stats. Not only are your fellow players likely to look down upon you for having such unbalanced stats, this character is likely going to find himself in trouble if he ever finds himself in a situation he canít smash through.
Worring only about yourself, never the group.
When dividing up the loot, make sure to split it fairly with regards to utility. A fighter should not be hoarding the magic scrolls and staves to sell off for gold when thereís a wizard who could use them. Likewise, when in a fight, failing to back up your allies will likely not win you the graces of the rest of the party.
Thinking every situation can be solved through force.
One of my favorite RPG books, Unknown Armies, opens their combat chapter with a section entitled "Six ways to stop a fight." If I could, Iíd repeat it here. If you have a competent gamemaster, you should be able to solve most disagreements without resorting to combat. Whether itís coming to a compromise, making monetary agreements, or finding nonlethal ways to work out your aggression, you should be able to solve a conflict without bloodshed.
Thinking up descriptive ways to use a skill not only makes the game more interesting, a generous gamemaster might give you bonuses for creativity. In the same vein, going in detail with an combat maneuver beyond, "I move here and attack," will, at the very least, help liven things up. Combat can be extremely slow, and using bland descriptions only makes it seem longer.
One would think that in a roleplaying game even the most mediocre of players would manage a little bit of character play. However, quite often players wonít adequately roleplay a scenario, instead falling back on their ability scores and skill modifiers to see them through. Thankfully, if youíve taken the previous advice to heart, solving this problem is usually as simple as putting it all into action.