If you haven't already, it's not too late to sow your sweet peas this week. You should have rich, fragrant blooms by the start of summer. The earlier you sow sweet peas the stronger the root system and more prolific the flower production.
I tend to sow mine in old toilet roll tubes, the depth encourages a deeper root system - you can buy root trainers that do much the same thing but I quite like the way the cardboard tube disintegrates when you plant them out, avoiding damaging the roots. If you haven't got any tubes to hand you can always sow several seeds in a 15cm pot, as I did with a few left over seeds. Just be prepared for some detangling!
Soaking the seeds overnight can speed up germination, but this year I'm trying nicking the outer seed coating to see if that makes a difference. After that, they're off to the cold frame and forgotten about till the frosts have passed.