In reply to Heike: I'm no expert but I have done various courses on training for climbing including 4 days with Neil Gresham several years ago. I can distill most of it down to three paragraphs of advice, but it may not be what you want to hear, given your comment about job/family getting in the way:
Volume of training - at your level of experience you ideally need to climb around 12-14 times per month (3+ times per week). If you can't get close to that amount, then I'm afraid you will really struggle to get any major physical training gain. Unfortunately, two amazing training sessions per week, will never beat four average ones, even if you do other stuff like run or go to the gym.
In short, go and climb somewhere, anywhere, trad, sport or bouldering
FORTY times before your summer holidays.
Intensity - don't worry about trying to train 'hard'. 90% of people don't do nearly enough endurance. Just focus on getting out and climbing something at ever opportunity. If you are short of time, repeat easy lines/problems to keep the volume of climbing high. The best rule of injury prevention is - DO NOT try any move more than
three times. As long as it doesn't detract from the volume of climbing, make as much of an effort as possible to do some or all of:
- a warm up/warm down
- some stretching
- core strength exercises (plank, leg raises etc.)
- antagonistic muscle work (e.g. 3x sets of push-ups)
Variation - Vary what you do. It is good to have hard weeks (climbing 4,5 or 6 days) and easy weeks. However, not be disappointed if you perform poorly after several hard sessions, just lower the intensity and keep climbing. However, above all keep enthusiastic and enjoy the climbing. Your goal is to maintain the total number of climbing sessions over the month but you won't manage that if the training is overly arduous, tedious and not enjoyable.
HTH