This first exercise is for your fretting hand. So I've given every finger a number (index finger being 1 and your pinky finger being 4). Rest your hand onto a surface and then tap in these kind of patterns:
You can make up your own pattern too. The sequence can also be longer or shorter if you'd like (2-1-2-3-4-3-2-3-4). The reason this is helpful is because it will benefit your dexterity (a fancy word that means the skill of your hands).
If you want make it even better for you, pull out your pick (if you don't keep it on you or just don't use one, use your fingers) and strum rhythms along with tapping your fretting hand. Here are some picking patterns that would be helpful (U = up, D = down, and R = rest):
Again, you can make up any rhythm that you want. Another thing I would like to add is that if you do have a guitar, try practicing these finger and picking patterns on the actual guitar. They will benefit you greatly if you can master these patterns. The reason why these patterns are great to practice off the guitar is because they can help you on the guitar.
Another thing you can do to practice is to pick up and air guitar (they're free the last time I checked) and jam with your music. Now when you're jamming with your music, try to really visualize you are playing guitar. Try to strum the rhythm the way the guitarist is strumming it. Try to finger the fretboard the way the guitarist is fretting it. You can also help out your ear a little bit if you try to imagine the sound of each note you play on your air guitar.
Listening will greatly benefit you. If you don't listen to much music, it will be hard to create anything. Imagine trying to write a book if you hardly ever read. Try to explore new music. You might find something that you will want to learn when you get back to your guitar. Also try to listen to all the instruments and not just the guitar. Listening to everything will help you if you ever decide to start recording. Another thing to listen to is the transitions, like how the band goes from the verse to the chorus. This will help you because you want to know how to transition the song smoothly.
Have fun and remember to tap, strum, and listen whenever you have the chance.