I'll be putting a row in this weekend and another row each Sunday for about 3 weeks. They usually all catch up but I like to think of some being a bit later than others. By first and second earlies rather than maincrop, unless you have stacks of space and enthusiasm for storing spuds.
Here's a good planting guide which might be helpful:
http://www.allotment....t-vegetable-chart.php
Enjoy you new allotment - runner beans, courgettes, red onions, salad leaves, I can't wait to get planting myself!