You cannot speed up the process entering a crowded map though, if it's full all you can do is keep on trying until you get in, there's really no other way. The failed to connect to map server message is VERY common in a full map and nothing you can do anything about.
But if it comes to other issues such as crashing or loosing connection it sounds like it would be down to your computer or internet connection. Sure the server can sometimes make users loose connection to a certain map or even crash but this doesn't happen often at all.
When it goes to the crashing you should lower your graphics settings for the game so it's less demanding on your computer, possibly try to stay away from crowded areas in general unless your computer can cope it, things like changing rendering mode for the game might help as well.
When it comes to the loosing connection you should make sure that your internet is not strangled by another computer or applications running on your computer such as streaming or downloading programs. Make sure you actually have a good solid connection as well if you use wireless internet.
All of the information you need to look into it can really be found here
http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=10423.0Some readin is required on your part though.
