Things I learned from socializing my latest chicks (who are now 8 weeks old and the friendliest and most docile chicks I have ever seen, they even like strangers!)
Always sweep your hand underneath them to pick them up since reaching in from above is predator like.
Food bribes from as early as you can. I started mine on grit at 5 days and broccoli buds on day 8. Plain yogurt was not a big hit with mine until I put a drop of red food dye in it, then they were nuts for it. (BTW, flavored yogurt has tons of sugar in it, it can be too much for little systems). One note, I only gave one small treat every day so the chicks don't peck at me all the time expecting a treat. They know one will come, they just don't know when
Just sitting next to the brooder, where the chicks can see you, talking with someone on the phone or even just reading a book helps because they get to know you as someone who is around but not necessarily after them all the time.
Letting them hop around on the brooder rim or lid while you just talk to them builds their confidence in people as it makes you seem less predatorish.
My tough cases I would bring over to the computer with me. I'd put a couple layers of paper towel on my lap and just let them sit on my arm, over the towels, while I typed away, basically paying little to no attention to the chick sitting with me.
Taking those steps, my chicks love humans and will flock to them to be petted and just to be near. They will let anyone pet them or pick them up, usually with no struggle at all.
The only thing I don't like about the way they have grown up is that they are not at all afraid of my dog or the cats and will actually run up to them (much to my dog's dismay :lol ). I would rather that they were more afraid since they will be free ranging soon and if they decide to run up on some strange dog it could be disastrous.
I do think their breed helped too since they are usually docile chickens, mine are Wyandottes. Although the silver spangled hamburg cockerel is just as docile/friendly and as I understand it that is not common for the breed.
I raised 8 chicks last year and they never became particularly friendly, but I learned a lot browsing BYC for a year and when I raised this batch I did everything to put them at ease right from the first day.