[Kajazy]

I'm trying to get my head around what to sow when and where this year...

Could anyone advise on which are the best crops to sow in succession to avoid last year's gluts? What works best with this? How far apart do I sow them?

Also, when do I sow the brassicas and chards etc that I want to be picking in winter? I sowed all mine in March last year and, with the warm weird spring/early summer we had, they were all ready to harvest by the summer!

[Trillium]

There is an excellent month by month explanation here:

http://www.allotment-garden.org/garden_month.php

[Yorkie]

Also the sowing and harvesting chart.

[mumofstig]

I sow things like lettuce in modules or trays and as soon as one lot has germinated I sow another lot.
This ensures a continuous supply throughout the warmer months.
I only ever sow cabbages 6 at a time and stagger their sowings as well, you may need more for a bigger family, but how many cabbages can you eat within a few weeks of each other, if they are all ready at the same time 
Sometimes it's easier to stagger harvests by using different varieties that are ready at different times 

For the other crops, it's mostly a question of freezing/storing any gluts.