Mid-summer seed sowing, how do you do it?

Howdy folks!   

So, as I head into my second summer with a vege garden, I'm sowing seeds for it in trays and looking ahead to the season as a whole.  Thinking back to my first summer one of the things that most stands out for me is the very disappointing results from direct sowed seeds.

My question to you all, is: just considering mid-summer sowings, how do you sow seeds?  Do you always start in trays and transplant (except for the ones which don't like to be moved)?  Or do you direct seed in the garden?  Or a mixture?  And, most importantly, why?

Last year, following the advice in both SFG books, I sowed directly into the garden except for the first lot of plants (at the time I started those, I didn't have a garden to put them in).

I've been raising from seed for more than 10 years (lettuces, to grow on my patio) so this is something I'm pretty good at.  Each time I sowed into the garden bed last summer I put seed raising mix into a little hole, tamped it down, watered it well, put the seed on top, and covered it lightly with more seed raising mix to the recommended depth.  Small sheet of cardboard over the square to prevent drying out, and checking every day.

However, my germination rates were terribly disappointing.  From memory way less than half of the direct sowed seeds actually germinated at all -- and the plants were nearly all very sickly, and in the cases of beets and chard, didn't do anything much at all.  I had one pea plant produce a single pod, from 16 seeds.

No doubt my results are partly due to the bought compost which I had to use for my MM (this summer I'll have plenty of my own) and to the terrible growing season we had last summer, with even commercial growers having a real challenge.  But the compost isn't going to affect the germination rate.

With direct sowing, I appreciated not having to look after seed trays all through summer -- I don't have a shed, or greenhouse etc, so it is a bit of a pain having to move them outside/inside every day.  But I also want better results than I had last year!  Should I really be starting in trays all through summer?

Wow, thank you as always for your comprehensive reply OG!  I'm seeing some more reasons why I had such disappointing results last summer.  (I forgot to mention that I spread Quash (our Sluggo) whenever I direct sow)  Guess I'm gonna have to look into improving my seed raising infrastructure!!