Keep your artworks out of direct sunlight. Your artwork might have a protective layer of varnish, but it is still possible for it to crack or fade if subjected to bright sunlight for long periods of time.
Do not lean anything against the surface of a canvas. Objects near a painting may not seem sharp enough to pierce the canvas, but it is always surprising what will cause a scratch or a rip. Prevent accidents and store your artworks away from anything that might press against the surface. Try not to lean artworks on one another when storing them. Separate them with pieces of cardboard to avoid damage.
Dust your artworks with a clean, soft rag occasionally to prevent dust buildup. Don't use cleaning products or water!
Hang your artworks away from very busy and possibly messy areas. Over time, artworks can accumulate a thin layer of dust and pollutants, airborne grime from cooking oils, particles from smoking and insect specks. If there is a place to display your piece away from these things, or where it will be somewhat less exposed, try to position it there.
Wrap your artwork well if you plan to transport it. Be sure to put a heavy piece of cardboard over the front and back to protect it. Then bubble wrap and place in a suitable heavy cardboard box. Rough handling can damage both the painting and the frame so pack it securely.
Try to avoid subjecting your artworks to extreme changes in atmosphere. Avoid excessive dryness, humidity, heat or cold. All of these conditions can affect the state of your artwork in a negative way (canvas puckering, paint cracking, etc.).
If your artwork does get damaged, don't fix it yourself. Take it to the place of purchase for a referral or look up a qualified conservator on your own. Amateur repairs can reduce the value of your artwork drastically.
Do not frame artworks on canvas under glass, because canvas needs to breathe, if it is framed under glass you may trap moisture inside the frame. Canvases experience small, subtle shifts over time due to mild atmospheric changes, so it is best to leave them without glass to allow them to flow with these slight changes.
Do not cover artworks with plastic for long periods of time. If there is humidity in the air, they may start to grow mold. Cotton sheets are best for keeping dust away.
Check the condition of your artworks periodically. Many people put up a artwork and forget about it, until they notice that it has been damaged. If a artwork is fading or cracking, a brief peek at it can prompt you to move it to a better place and avoid damaging it further.
Artworks on Paper
When taking care of art created on paper there are a few points specifically for preserving your artwork on paper.
Again, keep your artwork out of direct sunlight. If exposed to extreme heat or sunlight over long periods of time, paper can become brittle and reach a point where it simply crumbles to the touch.
Frame under non-glare glass, treated with a coating to protect the work from UV sunlight if possible. This not only protects your artwork from sunlight, the non-glare glass makes it easier to see the artwork surface when it is displayed.
The mat and backing of your frame should be made of acid free paper and finished with acid free tape. This is to avoid any moisture reaching your painting and damaging it.