1) Professionalism
This is a key issue. It's important how you act when being an accredited photographer. There are generally rules and regulations, many of which are unsaid.
More and more, it seems that certain professional guidelines have to be written.
1) Only apply for access/accreditation if you plan to attend the event.
2) If, for any reason, you can't attend the event you're accredited for, be professional enough to let the organiser know.
3) Watch for other photographers. Even if it's not your first gig, in general, others will have more experience. See what they do.
4) Stay off the pitch. Unless you are told you can go on to the pitch, stay off. Stay along the touchlines.
5) Give the managers space. Stay a clear distance from the dugouts or managers seats.
6) Don't block someone's view. In general, when seated behind the touchline, those nearest the corner sit closest to the line. Those nearer the goal sit further back, so that the person in the corner has a clear view of the goals. It's just professional courtasy.
7) Remember any restrictions - some associations put restrictions how/where your images can be used. Always remember to abide by these rules, since breaking them can end up with you being blacklisted.
8) TV/Advertising - at larger events, make sure not to block advertising or the view of the TV camera.
9) Officials - stay out of the way of all match officials, and listen out for any specific instructions.
10) Press briefing - if there is a press briefing, make sure you attend. There may be specific restrictions or information for a particular event.
The more professional you are, the more respect you will gain, and the more friends you will make.
If you break the rules or act unprofessionally, be prepared to accept the consequences, but also don't forget that your actions may also impact on other photographers.