Allotment Gardening

Hello! This is my first post!
We got our allotment last year and true to form were not able to grow carrots. I've NEVER been able to grow carrots! We have pretty heavy Devon soil and the bed I've planned them for cracked last week after the first week of dry weather. I guess I need to improve the soil structure a little before planting as the same happened last year (before it rained solidly for 3 months) and the seeds never sprouted, but wary of adding too much enrichment for the carrots as I read they don't like that sort of thing. How about a bit of compost and a bit of horticultural sand? Is there anything else I can do to try and help them on their way? Tips for sowing the seed? When would be best to start them - not too early?
The bed has overwintered onions and garlic growing happily already and I reckon I have space for 3 rows of carrots.
Thanks for your patience with a beginner. We did manage a fine harvest of potatoes, garlic, strawberries, raspberries and a ton of slugs, so aiming to better that.

I have never had good lines of carrot in the ground.

If you like small carrots (dislike the term baby applied to veg) grow in a large container of compost /sand mix .
Sew close together water and cover with polythene which you remove when the plants are 2"-3" high.
When the poly is on do not let the sun cook them!

No carrot fly just wall to wall little carrots.

i used to get very severe fly attacks, to the point where i stopped growing carrots. now, i use tall plastic barrels filled with soil (over 3 ft) and wrap fleece in a cone at the top. not lost a carrot for 3 years now. i empty top 18" of bin every year and replace with sieved soil (molehills normally)

Grow in trugs filled with spent compost with a little fertiliser added to give it a boost. Or just use fresh multi purpose, pass it through a sieve first  if you want corkers.

Totty