What to do depends on your plans and objectives.
If you want to rush in and have a small trident bonsai reasonably quick you should start pruning. Let shoots grow to 4-6 pairs of leaves then trim them back to the 1st or 2nd leaves. New shoots will form from the buds at the leaves. Let them grow to the same size then cut again. grow and cut as often as the tree will allow. That will give ramification and density to the branches. In winter when you can see the structure properly do some structure pruning to establish the best framework possible. Repeat for a few years until you are happy with the result. You may need to wire some of the branches into better positions. Do that before they harden too much and remember to keep an eye on the wire and take it off before bark damage ruins your work. If branches are already hardened and in wrong places cut them off and work with the shoots that will grow in place - 1 step back to go forward on a better path.
Feeding the tree well will allow more growth and more trimming so you can reach a goal faster.
If you would rather have a trident bonsai with an impressive trunk you should just let it grow as big as it can grow. Planting into a larger pot or into the garden will give faster growth and a quicker result. Each winter prune hard to give the developing trunk some bends and taper. I also root prune each winter to establish a good nebari. When the trunk is thick enough for your liking transfer the result to a large pot and grow branches and a new apex. Follow the first method to get good ramification.
2 different results from 2 slightly different methods. Your choice which way to go.
Note that not every tree grows into a great bonsai, even in the best hands some just do not work out so look at every tree as possible bonsai and something to learn on. Don't be afraid to scrap any tree that is not performing and move on to something better with our developing skills.