If you apply to a guild as a cross realm applicant be aware of the extra hurdles that you face. Whilst it often impresses a guild that you are prepared to spend money to join their guild, there are some drawbacks. For starters you are leaving all of the people that you know. This may seem obvious but the implications are perhaps overlooked. Your new guild may be very welcoming and helpful but it is unlikely that they will be free to help you with all of the group activites that you did with friends on your old server. Most guilds run groups for the daily heroic so that will not be a problem. But what about that weekly TK mount run that you did with your mate? What about that rated battleground team that you had just found? That herb supplier who always gave you a great deal which allowed you to create and sell flasks for a profit? All of these unappreciated contacts will be gone and you will have to spend time and effort finding new ones.
You will need to establish yourself again. This is not neccessarily a bad thing depending on your reputation on your old server. Perhaps you were a well known name on your realm’s forums. That will not be the case on the new ones. Essentially you need to treat the move as if you are moving school or taking up a new job in a different workplace. You need to present the best side of you and make a good impression. This is especially important within your new guild but also pertinent is the impression that you make with the general population of the server. A bad reputation can be made very quickly and will get back to your new guild’s officers before you know what is happening, especially on a low population server.
You will need to acquaint yourself with the new market of the auction house. Prices are almost certainly different to your old server which could be a source of some extra gold if you do your research before transferring. Buy items whilst still on your old server that will sell for a profit on the new server to get yourself some hassle free gold. You could lose a lot of potential gold if you do not research prices on the new server before transferring. That stack of heavenly shards that you had stockpiled could now be worth 50% of the price paid on your server. Just create a level one character on the new realm before transferring, run him to the auction house and have a browse.
Transferring is not a bad thing. You just have to make sure you check out the realm fully before moving. Check the dungeon finder queues, bg queues, number of PUG raids advertised in chat and their progression level. Check the number of advanced raiding guilds and the state of the arena scene. Be prepared to put in the work to create a good persona and a good impression and it will pay off. Transferring server to join a better guild can sometimes be inevitable if you are on a low population or poorly progressed server. It does not need to be daunting. See it as an opportunity to reinvent yourself and to meet new players and you will be fine.