I like learning such things from a book. REI does some classes and you can probably find some outdoor organization that have classes too.
One way to practice is to get out in a park and run triangular courses and see if you can end up in the same spot. Try it with a hood blocking your view so you can only see the compass and a little ground in front of you. You will be counting steps to estimate distance as well as mthe compass direction. A soccer field makes a good practice area. Most books will have some suggestions for practice.
You can test your triangulation skills in town using tall buildings, broadcast antennas and water towers. You can use a smart phone or GPS to confirm your results.
It's really a process of understanding the angles and adjusting for declination. In the field, taking regular bearings and following your progress on a map will avoid needing to do things like triangulating on peaks. If you do need to go there, following your progress will let you know which peaks you are looking at— something you need to know to get your location. In other words, don't wait until you are lost to get out your map and compass!
I enjoy the process and having a map in hand lets you know what features are in your view. I've been working on getting to know all my local peaks I've lived among them for a lifetime and its fun to be able to name them as well as have a feeling for the trails, lakes and rivers around them.
This is the sort of thing you have to put up with in Seattle. I know a few of the major peaks:
