Get over the feeling that you aren't an artist. Remember when you were a kid & could paint with unabashed pleasure instead of being so concerned with the end result.
If you don't know how to paint don't worry. Instead of trying to paint a house or even a river, go for the emotion that these create in you, or use the colors that inspire you. Modern art is about loose interpretation.
Keep a tight color palette. Use a bright white background & spatter one or two colors on it. If you use primary colors like red, yellow & blue it can seem more like a kid's finger painting.
Less is more. Some of the most famous works of modern art are simply splashes of paint, squiggles or dots. Don't worry about precision, try & have fun.
Add more substance to your work if you have small canvases. You can create a series of paintings that will hang all together, just varying each by the background color. If you have three skinny canvases, push them close together & paint as if it was just one canvas. This is called a triptych.
Layer paint. If your work seems too bright or muddy, all is not lost. Try layering neutral colors over it after it's dried. Work in thin layers so parts of the background show through.
Modern art work always needs a crazy name so people can tell what it is. Try putting the name of your pet followed by your favorite color & then the year of your birth.