I think it just has to come. You can't force yourself to put emotions into music. It has to flow naturally. 
You can set a goal of making a sad or happy tune but IMHO that's not putting emotions into it.
My music is trial and error too (even with basic theory knowledge) but I think after some time it will come itself and I'll be able to put emotions into my music without knowing it.

In my late 20s when I went back to writing aggressive rock music, I had to dig deeper and think about what kinds of topics actually spurred the emotions that my music thrived on.

When I was in high school it was people I saw every day who pissed me off, frustration over my relative lack of freedom, etc.--stuff that was always in my mind, bubbling up to the surface day in and day out. As an adult, I don't think I ever encountered stuff that actually made me that angry, or at least not more than once in a blue moon.

So instead I started writing music about the stuff I was thinking about that struck me as interesting, and then I'd put an angry edge on it. For example I was thinking about the heroes I had as a kid (Kurt Cobain, Layne Staley, etc.) and how now that I was the age they died at I could realize what total assholes they were, how they abandoned their families (and now that I had a family of my own I could appreciate just how fucked up that was) and how they stood for causes that are actually really destructive. In the future I could see myself writing a song about the failures of atheism, or the complacency with which people give up their own privacy online.

In a way the topics inspiring my music became less personal, though it was always still stuff I'm passionate about and interested in. The upshot is that I think my subject matter became much more unique and interesting (not that I ever wrote songs about girls or partying...). How many rock songs get written about this stuff?

Any tips on involving emotion to my music?

So to sum it up, don't think too hard about the emotions, and concentrate on the broader question of "what do you have to say?"

I don't say music theory knowledge is a necessity. There are many people who make beautiful songs without knowing the theory. But as we are talking about getting emotions into our music, I just think it's advantageous to know at least some basics. It can only help.
On the other hand you are absolutely right about listening to different genres of music. I can't stress enough how important it is.

Try making a song when you're emotional already, it helps to know basic chord and scale knowledge because then you can focus more on the emotional part .. Get a midi and play with chords when you feel real happy or real angry/sad and see what happens

When I'm trying to put an emotion into a song what I do is use certain sounds and effects that kind of give me that emotion. Not the entire song will be like that but maybe you have a pluck sound that gets really sad when its in minor chords with a certain flanger effect on it. Or samples. Also the arrangement and things for white noise etc. I have an interlude that I made and for me its pretty emotional because it uses rain that I recorded outside my window as the white noise in the background along with this epiano sound that I put lots of reverb on.

I think it comes naturally man. Usually in retrospect and then it starts to become intuition. When I'm getting that mojo to start writing I follow that 100%