If you feel like you're getting stuck in the same old I IV V chord progressions you've played over and over again, you're not alone. You can make your songwriting better and playing more fun if you learn how to juice up your chord choices. Let me give you a couple easy tricks to get out of that rut.
Trick #1: Change just one note in the chord. Take a basic chord form, either open or barre and tweak one of the notes either higher or lower by one or two frets. You'll end up adding an extension to the chord, ie. 9, 11, 13, sus, diminished, etc. The exact name will depending on which note you're adding to your chord. Don't get stuck thinking about theory at this point. let your ear guide you to some new sounds and figure out what it is later.
Trick #2: Change everything except one note. Every note in a chord has a particular job. And you can change its job by changing all the other notes around it. Try this first with notes either on the top or bottom of the chord since those are easier to hear. Let's say you're playing around with a G major chord and B works nice melodically. That B can become the root of the next chord (B major), the 5th (E or Em), the 7th (Cmaj7 or C#7), the 9th (A9), the 11th (F#11), the 13th (D13), or a sus (Gbsus). That's a whole bunch of chords to pick from and you can choose whichever sounds best to you.
Trick #3: Grab a random selection of notes that, on the surface, don't belong together. Any group of 3 or 4 notes will work well here. Try the chord both strummed and as a picked arpeggio. This is especially useful if you're looking for interesting dissonant sounds.
Trick #4: Mix some open strings in with the chord. Take another of your basic open chord shapes. Try moving that shape around the neck and you'll find all sorts of nutty chords. You can also do it with barre chords. Try this one. Take a basic major barre rooted on the 6th string, but open up the two strings. Move it around and hear how those open top string interact with the other notes each time.
When you get stuck for inspiration, you don't always have to go to the theory knowledge to find a new avenue. You can start banging around using some of these tricks to ignite the inspiration you started with. I've written loads of songs around mistakes and accidental chords. Once you've given the song some structure, then you can go in and take a closer look at the theory to see what you're actually playing. You might find you're a lot more advanced than you thought!