If you have a goal to make more art or you're not feeling very inspired or motivated, and need to get your creative juices flowing, these exercises can help.
Make a series of small pieces under a time limit: Set up a board with a series of small pieces and give yourself a time limit to paint each one (e.g. Six 5x7" pieces, with 30 minutes for each one). The size of the piece and time you allow yourself can vary depending on how large and how fast you normally work. Once the time limit has expired move to the next piece, try not to worry about the finished level or skill in each piece, just keep painting. The idea is that you end up with a series of small pieces that will help you loosen up and feel inspired. After a day or so, evaluate each piece and decide if you want to give yourself more time to work on it, use it as sketch/reference for larger more finished pieces, or consider it practice and move on to something else. You might also discover that these small pieces are actually finished and don't need anything more at all!
Make a visual translation of a song: Pick a song or an album that you like and paint from your imagination while listening to it. You can work in either an abstract or representational style, just paint whatever feelings or images come to mind while listening to the music.
Explore new ways of working: Make four (or more) versions of the same scene using a different method for each piece. Do one piece the way you normally would then go wild with the others; choose a different paper, try different underpainting techniques, use an entirely new color scheme for each one, or even choose different mediums all together. Allowing yourself to explore is a great way to boost creativity and get inspired. Seeing the same scene in different ways might spark new ideas about how to work. At the very least, creating the same scene over and over will take away the guarded feeling artists sometimes have to "not ruin a piece" because it feels special. Removing that pressure lets you explore, which can boost your creativity.
Limited Color Palette: Choose 8-12 pastels, or 3-4 tubes of paint and try making a painting with only those colors. You can mix and layer colors to expand the palette's range. Make the exercise even more challenging by working with colors you don't normally use. Forcing yourself to work within limits can help push you into a more creative space.
Crop one photo into as many different paintings as you can: It can be a really fun challenge to use one reference photo as the inspiration for lots of different paintings. Think about zooming into a photo and just painting one small area instead of the entire scene. Make a vertical painting from a horizontal image. If you have a landscape photo try just painting the sky, then paint only the land. Not only can this boost your creativity in the short term, but thinking about ways to change reference photos instead of just replicating them can help you remember to not be overly tied to reference photos in the long term.
I use these exercises whenever I feel a lack of creative motivation and want to shake up my usual habits. They really help me to feel inspired. If you need a creative jump-start, give them a try. (And if you do, leave a comment and let me know how they worked for you!)