I may be pretty new to this, but I would recommend that you get a solid grasp of harmonics and keys in general.
Choose a key, like G major for example, look at what notes are part of that key (all flat except F sharp), then select a few chords from G major (like the typical I, ii, IV, I, which in this case is G, Am, C, G) and play those chords/arpeggios/bass/whatever using those notes as your background. Improvise on top of it using notes of the G major key that relate well with the chords you chose. Try to find patterns you like and vary them. One way to know that you got sufficient theory for me is to see if you can do those 2 things :
1) Improvise a song on a real instrument. If you use the piano, keep a simple pattern on the left hand and choose a rhythm you like, then improvise on it with "correct" notes with your right hand
2) Take a song you like and can play on an instrument and decipher it. Look at which chords they used and which key it's in. The key can be found using the key signature, the first and the last chords (usually). The chords are usually pretty straightforward in the background. If for example the background plays E G E G E G E G | E A E A E A E A you can be pretty sure that the first measure is either C or E and that you second measure is A major or minor. You can see if it's C or E based on the melody and whether it's A major or minor based on your key. Once that's done, us the roman numbering and play the song in realtime with a different key signature but with the same roman numbering (google it).
Once you become proficient in those, you can quite easily know which notes you are "allowed" to play at what time and you can spend a lot more time on tuning your instruments as you want, adding effects and beats. Make full use of harmonics. An example is the first song I made :
https://soundcloud.com/user-133453329/p ... -1/s-IiO5f. You may or may not like it, but the song itself was written quite easily. I chose a random key, 3 chords (I play Chord 1, Chord 2, Chord 3, Chord 2 (short), Chord 3 (short) and repeat) and I'm basically just making sure that I play notes from those chords.
Finally, something regarding LMMS and music in general, but not music theory:
* Use automation, fade your songs in and out, boost your bass at critical times or at transitions, ...
* You can automate other stuff than volumes
* Filters are interesting
* Minor songs are usually more intriguing in my opinion
* You can superpose several times the "same" instrument but configured differently. Adding/Removing them at key times can be neat.