Maintaining your surveillance system is a good habit to get into, by staying on top of your surveillance system you'll always know whether or not it's preforming optiomally.
If you have outdoor cameras, make sure you're reviewing the outside footage. Vines, bushes, trees can easily interfere with optimal vantage points, keep these obstacles trimmed and neat in order to keep your camera angles unobstructed.
Clean Camera Lenses
Make sure to check your indoor and outdoor camera lenses periodically to insure they're clean. Look for any dust, smudging, or other natrual residue that may accumliate on the lense. If the lense is dirty, you won't get a clear shot even if your security camera shoots in high resolution.
To begin the cleaning process you can use a can of compressed air to lightly spray off any dirt or dust from the lense followed by wiping down the lense very gently with a microfiber cloth.