In reply to neuromancer:
Your first decision is:
1. Am I climbing for fun?
2. Or do I want to get better?
The reality, for most people, is that it's 1. but their ego is telling them that they should get better. So they start on ill-thought out training programmes, get injured, etc.
If it's 1. then just enjoy it, whether it's once a week or more/less.
If it's 2. then, if it's just once a week, more important than the interim, is how you spend the session. You'll need to focus on where you need to improve, whether technique (always a good first port of call!), power, endurance, whatever.
Then do what you can to back up your weekly session. For most, it will probably be simple stuff, maybe a little aerobic, plus general/antagonistic body conditioning exercises. (The four best I know and do are push ups, sit ups, leg scissors/crunches and sidebends - no more love handles!)
Pull ups, maybe. A finger board - be careful, to be treated with great respect. A campus board, forget it unless you're bouldering at least V6, imho.
Be careful!
To doubtless slightly misquote, 'The thing is to get strong - but not get injured!' (Wolfgang Gullich)
Mick