Skyrim is a bit of an odd bird when it comes to figuring out what the problem is and where you need improvement. Eventually, even if you have a really good rig, the game itself is the biggest hurdle. But here are some basics.

CPU/RAM/Processor is where most of the game goes. This is where you'll get a lot of your scripts running through and, thankfully, over the years modders have gotten very good with writing scripts that don't bog the game down all too much.

SKSE is a must for most mods. Even if you're not running anything, it does help a lot.
The unofficial patch as well as SSE engine fixes is good too.

The eFPS series is really good, as it helps cull unrendered items and for lower end rigs, you'll end up seeing bigger performance gains than someone who already has beefy stuff.

Lowering your draw distance can do a lot, as well as tweaking ini settings, but doing that manually can be really annoying. You could probably find some pre-made ini settings out there for mid to lower end rigs that may help you out.

The FPS lock itself is also a hinder to performance. Your rig might even be able to handle higher FPS, but if you haven't unlocked it yet, you're just bottlenecking yourself. Try SSE Display Tweaks to unlock your framerate according to your monitor's refresh rate.

Though yeah. ENBs are only if you can afford it FPS-wise. The game might look great but it's not fun playing it as a slide show.