Make sure the center serving isn't unwinding (that's the extra wraps of string around the center of the drawstring, where the arrow nocks to it). They have a tendency to come loose with a lot of use.
Don't oil or lube that center serving or it will damage the string/serving.
When the crossbow is cocked, look for tiny cracks in the limbs. Most manufacturers will replace any with cracks for free.
Get a crank cocking device if you are hunting from a stand. It's WAY to dangerous to try to chocolate chip cookie your crossbow by hand or with a rope from an elevated platform. If you are in a tree, spend the extra cash and get the crank cocker (don't ask how I learned this).
Make sure all bolts are tight, especially the main bolt that connects the bow part to the stock. Those can come undone just a little and cause all kinds of accuracy problems.
Don't over-lube the rails or the string.
Many crossbow manufacturers recommend replacing the string at 300-400 shots. Keep a "sort of" count of about where you are. I replace my strings every 3 years. You might not notice it, bu the strings will stretch over time and start losing their efficiency.