I’ve been focusing on modeling technological things like ships. Should I do tutorials on modeling humans and complex stuff like that? Will it help?
I can only speak from my limited personal experience using blender so others may be able to give you a more detailed answer.
Modeling organic things like people and plants is very different to modeling man-made objects. So I would say that it depends on what it is that you wish to achieve with blender. If it’s simply about improving your modeling skill then by all means go into modeling people etc. but if you have a specific application for blender that doesn’t involve people or animals then I don’t think tutorials like that would benefit you very much.
I agree with what Peter Scott said 
But if you are learning Blender for fun, I would say start with hmm a mushroom and work your way up to humans. I am currently modeling a tree as an asset for my game and I have to say I hate modeling people because I am not very good at it. So yeah you can easily start modeling a bit more complex things and experience alone will make you better 
Just be careful when modeling organic things, they are not completely symmetrical or perfect 
More technique you know better modeler you will be. Ship hull or car body can be very organic in form, although they are man made stuff.
If you model people, then you can put them in your ships and other stuff. You could even learn to animate them(If you don’t already know how to) and make an animation. Being able to create people, even just having a couple stock characters that you use opens up a few possibilities when it comes to story telling. They don’t have to be photo real, they could be cartoony. It might be best if they are cartoony because you don’t have to fight the uncanny valley.
If you are not interested in telling stories with people, or integrating them into your tech renders, then modeling people might not be as useful to you other than as an exercise to improve modeling skills.