One of the easiest ways for a print to fail is if the material separates from the bed. There are expensive sticky sprays you can buy, but cheap hairspray can be easily used to improve adhesion.
Step 1: Choosing the Hairspray
Get hairspray. Find the strongest available, usually level 10, or "extreme hold", or similar.
Step 2: Heat Up the Bed
The hairspray sticks best to a hot bed. It will work on a cool bed, but for best results heat up the bed to about 50 C.
Note: Hairspray is flammable. Most operating temperatures for printers are well below the ignition temperature, but don't try to move the printer while applying, as sparks could ignite the spray.
Also, keep in mind that the sprays specifically for this purpose are made of acetone, which is also very flammable, but it is still good to be careful.
Step 3: Spay the Bed
Spay a layer of hairspray on the bed. Try to get an even layer.
Step 4: Let Sit
Let the hairspray "cook" for about 30 seconds to a minute.
Step 5: Wipe Off
Use a paper towel to wipe off excess spray. Try to lay the towel down flat and absorb the spray, don't actually wipe it off.
Step 6: Test Stickyness
Touch the bed. It should feel sticky to the touch. If not, repeat the process. Try sticking up areas of the bed individually. The bed will now stick to prints much better and prints will have a much smaller chance of peeling off, and you probably won't need to print with a raft. You will probably need to reapply every 2-8 prints.