I started off with just guineas, they were so scared of me. So I went out and got a bunch of chicks too. When the guineas saw that the chooks weren't afraid to approach my hand they got a lot braver. It took them about a week to get used to my hands, I made sure that every time my hand went in there, I had some white millet (make sure to provide them some grit too if you feed them treats), now they jump on my arms to get to the treats.
I changed my brooder once a day. My friend has a lot of grass clippings from his huge lawn, so I had an endless supply of dry grass bedding. I did read that chicks could die from digestive issues from ingesting the grass, so I provided them with chick grit and haven't had an issue with that. a good thick layer of grass bedding kept things much more sanitary...
To have the guineas associate positively with handling, I always put treats in the holding bin I was moving them to when changing out the brooder. It wasn't long before they stopped struggling when I cupped them in both hands, where before they would struggle and kick (they have such strong legs!) they now simply relax and allow themselves to be transported. Also some treats in the brooder when I moved them back (when I could be bothered) helped strengthen that positive association.
They're older now, and it hurts to have them jump on my arms, so I don't let them do it anymore. If they see my hand coming, they would still avoid it nonchalantly, but occasionally I can get a pet or a tail tug in when they are distracted since they're not on guard when I'm around.
Also I just want to note that I never chase down my guineas. These days I bring them outside in an enclosure during the day, and occasionally allow them to free range when I have time to sit out there and watch them. I bribe them back with a treat or wait for them to return enclosure when they are hungry. They stick to each other like magnets, so once I have most of them in there, the rest will follow.