Hi and welcome! My first, obvious, hint:
Make sure you read the rules. Then discuss them with your friends, read them again. Make sure you all understand them to the full extent.
Second would be on the clan part. I would advise you to KISS. Keep It Simple Stupid. Lots of big gangs have come and gone, the bigger they were the sooner they were gone (with some exceptions ofcourse). If you are with a core group and know eachother, keep it like that for a while. It makes life easier and will most likely prevent reports for rulebreaking if you don't take any next random player into your group.
Thirdly, a advice that may be more dependent on the sort of player you are.. Make a clear goal for your gang. Who are you, what are you. Don't aim to high (f.e. We will always be at the processor and everyone needs to tax us), because that will be your downfall. In this as well, keep it simple. Figure out a cool name related to what you do and stick to that, with the maximum amount of roleplay possible. If you can manage to hold a relative small, controlable group, with a clear cut RP goal, you will find that playing on this server is really enjoyable and provides great roleplay!
However if you are the next best group who takes anyone on, go about in Ifritts as soon as they can afford them and rob and kill everyone they can find, even if it is in RP, life will be hard, encounters will be unfriendly. In the end it is all up to you. We all need money to come around, but it s not always the best thing to take everything off someone. Remember, if you let them have a bit, it will be fun for them too, so you will have a chance to rob them again. If you keep taking it all, they might leave the server because they can't get started!
And a third and last advice;
Roleplay the fuck out of us =)
Have fun and good luck !
Oyeah, you dont NEED a rp name, but as you might have figured it would be more awesome and make your encouters better. If your name is IAmThEBEST!@266233 that might be awkward ingame when you introduce yourself.