Clearly mark any Out-of-Character remarks and game mechanics, and separate them completely from descriptions. This helps make your posts more understandable, and helps maintain a sense of story. It sometimes helps to provide a "Summary of Actions" and "Status" section, to track all of the game mechanics (actions taken, HP, condition, ammunition, etc) at the end of your post; it may help to enclose this Out-Of-Character information in a "QUOTE" tag.
Even in "Free" games, it is rude to hijack a thread. Try to "join" the ongoing roleplay, rather than start your own line of action. Roleplaying is about interaction.
Player killing is generally in bad taste and is actively discouraged (through XP loss). Tension between characters can add interest. However, at the end of the day we should all be respectful and friendly towards one another.
Out-of-Character arguments stay out-of-character. In-Character arguments stay in-character. There is no reason to drag past bad experiences into the game.
In general your posts should follow some general conventions that have come to be standard here on the boards. Proper tag use is important to the readability of your posts. to use a tag either click on the appropriate button above the text box, and don't forget to click it again when you are done with it. Or you can manually type it in enclosing your command in brackets, [tag] and ending with the same command in brackets preceded by a slash, [/tag].
first when quoting another post of course use the "quote" tag. This is generally speaking the first thing in your post.
After that you have the main body of your post. If your character is thinking something that is generally placed in italics using the "i" tag. Speech and only actual speech is placed in Quotations "Speech text", it doesn't matter what language you are using , that is covered in a description of your character speaking or certain assumptions can be made, for example a wookiee speaking can be assumed to be speaking in Shyriiwook, the only language they are capable of. You may occasionally wish to link text in your post to a website. This is done mostly when referring to something that other players may not be familiar with but their characters should be, most often some entry on wookieepedia. This is a little different than other tags when you click on the "URL" tag it will pop up a little box in which you enter the URL you want to use. this will show up (in brackets of course) as "URL=www.whateveryouputinthebox.whatever" you then put the text you want the link to be and close with the "/URL" tag.
Finally if you wish to take some actions that have mechanical effect you will put that at the end of your post also using the "quote" tags.
Most commonly you will state the action type, for example Standard, Move, Swift, Free, or Full-Round:then your action, you will also link any needed dice rolls here for the most part if you use invisible castle or some similar website they will have an option to format your dice rolls for bulletin board use.