TL;DR: comb your scalp systematically with your fingers, wash your hair to remove them from hair (be careful with laundry carrying ticks home too), and try to catch/prevent them getting into your hair in the first place.
Great question. I worked in the woods with long hair under a hard hat, and wow did I accumulate ticks. I'd reliably find >5 per day. I did end up getting Lyme, thankfully diagnosing and treating it early - I share that caveat to say, take my advice with a grain of salt! Still, I got a lot of experience finding ticks from that. When I was in tick prone areas, it became habitual to do tick checks of two sorts: 1) in-field quick checks to clear off clothing, and 2) end of day thorough checks to clear off body.
1) In the field: At any breaks in the day we would do a quick 'pat down' of ourselves, quickly touching and visually inspecting our bodies from head to tow. Hair was mostly neglected in these checks, but getting rid of ticks you spot in these checks reduces the chances they'll be able to settle into your hair. An important note about hair and all body parts is that we kept mostly covered, even despite brutal heat and humidity, to avoid ticks and other bugs. Pants tucked into socks, shirt tucked into pants and outer shirt over that, sometimes gloves and bandana mask when bugs were very bad. I had long hair, and I learned the importance of neatly tying my hair up in a bun resting at the back of my head and tucking it under my hard hat. For one, hair gets messy in the woods in general, and two, the way hair accumulates messiness can also accumulate ticks. Don't give them any easy platforms to catch on to, and keep your head and hair out of the bushes and grass they linger in if possible.
2) At home: Pretty soon after returning home, some privacy and a shower is necessary. Put all your clothes in the wash and/or dryer ASAP (or store them separate from 'tick-free' areas at least), clean yourself off, then touch every inch of your body with your finger tips head to toe. Get in the habit of being excessively detailed about it, you want to see and touch every part of you to catch any little bump and inspect it. It's good to get in the habit of inspecting yourself anyway. Showering before thorough inspection is helpful, especially with long hair, as the soapy water can release loose ticks from hair. When you inspect your head, the same principle of detailed inspection applies: touch every part of your scalp, combing it carefully with your finger tips. Do this systematically in rows so you cover every spot of your scalp. If you washed your hair, you've reduced the chance that some ticks are stowing away there. With long hair, doing additional feel-throughs while it's clean between trips to the woods is a good idea to catch stragglers.
Other than that, keep an eye out for symptoms and bullseye marks when you've worked in a tick prone area. Lyme is unpleasant but what makes it really debilitating is misdiagnosing it for months or years: if you have potential symptoms, insist on tests or preemptive treatment.
