I suggest you to read those couple of golden threads about arrangement and song structure:
http://www.dogsonacid.com/showthread...hreadid=264521
http://www.dogsonacid.com/showthread...hreadid=274688
http://www.dogsonacid.com/showthread...hreadid=244758
This really improoved my arrangement skillz when i was stuck with 8bar loops,
and i still think that arrangement is not something you learn,
it's something that should come naturally.