By High-sec WH I'll assume you mean C1-3 WHs with High-sec entrances, because ALL WHs operate with the same legal system as 0.0 (meaning, there's no CONCORD to come to your rescue, ever). The above link to EverythingWormhole is a very good guide, I've got a copy of it I read myself. I also use the Wormholes and WH Systems pages of This Site
to get an overview of the particular hole I'm going into at the moment.
With regards to the Myrm for WHing, it's doable but not as much so as the other races' tier 2 cruisers because Sleepers will target drones. You're going to need to rely on rails for damage and have a good omni-tank. Personally, I use a Drake that can passive-tank well for WHing. From what I've seen, the Drake, Harb, and Cane are the best ships for doing things in C1-3 WHs (T3s would be better, but they require much more ISK and skills to fly).
I'd suggest reading the above posted guide before jumping in and stick to C1-2 holes 'till you get a feel for it, a Myrm should be able to handle those fairly easily as long as you're not relying on drones for your DPS and have a halfway decent tank.