This is probably the most important aspect of composition, making it enjoyable. By this, I don’t just mean making a piece that is enjoyable to listen to but also just as fun to play.
I don’t mean you should make it super complicated or anything although that may work too. Sometimes even simple songs that seem to connect better with you would make it all the more enjoyable to play than having a shred solo at 200bpm which has no meaning.
Using different chords, rhythms coming up with a cool solo and creating any kind unique sounds that you probably would not generally hear would give you a sense of accomplishment making you like what you play.
Adding embellishments apart from just adding to the feel of the song, is also a great way to make songs more fun to play.
Adding passing chords to connect chords (For example, In the case of a piece in A minor, adding a C#mi7 before playing Cmaj7 to jazz things up), accenting notes, arpeggiating your chords, harmonizing riffs (you could also try harmonizing different instruments together.
You can see this in the solo for “Downfall” by Children of Bodom where the keyboardist and guitarist harmonize). If you know any theory, that’s a bonus. Using unusual chords, time signatures and techniques sometimes makes it fun to play.
What you may want to avoid, is repetition especially when you’re just using simple riffs that might just be chords or something else just as simple.
Now, I am aware that a lot of music nowadays is very repetitive and all and some of you may believe that repeating something makes it easier to comprehend making the audience more attracted to that.
I’m not saying that it’s entirely wrong.
Although, I personally believe it is sacrilegious to make multiple sections of a song sound entirely the same. However, I am not implying you need to change your riff to make it sound different.
If you are satisfied with what you have composed even if it is extremely simple, what you can do is add more elements to it when the part is repeated.
In another song that I composed with Dayve called “Judas”, you would notice that the guitar parts in both verses sound exactly the same but this time it sounds different because there is now another guitar part soloing mildly while the highlight is still the vocals for which there is a new part too which is harmonizing to complement the main vocal line.
Similarly, you could try adding things that you didn’t have earlier.