It's important to find the balance between letting your other engineers design and implement the more interesting and challenging problems, and also making sure they don't get in over their head.

Sometimes tech leads (often rightfully) assess that they are the best engineer in the room, so they should tackle the hardest problem. I don't think this is a good idea most of the time!

Giving ownership and autonomy is often one of the easiest ways to increase someone's productivity, so let your team take ownership of the parts of the project they are interested in.

Often a tech lead might end up having to take on the least fun tickets, the drudgery, yak shaving, etc. while the engineers working under you will get assigned work that has more prestige/glory. This won't go unnoticed, and will be appreciated by your team.