Firstly let me say that most common species of snake will eat without hesitation and it's definately not my intention to do any scare-mongering.
However, no matter what you do, you may from time to time find your snake won't eat - so what should you do?
To start off with don't get too concerned if this in the first time and your snake has eaten recently.
Your snake may just not be hungry, or might be about to change it's skin. As this moulting process can be uncomfortable some reptiles (including many snakes) stop feeding a few days to a few weeks before the shed.
If your snake does shed, it does no harm at all to miss a normal feeding day then start again the next week.
Other reasons for your snake not eating for longer periods than one or two feeds could include that it is being kept at an incorrect temperature, that it is overly stressed such as from overhandling, repeated loud noises or other larger, more aggressive snakes in the vicinity.
Consider each of these in turn, trying to see if you've done anything different recently, that you can put right.
Have you installed a new heater or put a new stereo in the room with your snake for example?
Is the heater working at all, or has it stopped working?
Another reason could be an illness of some form so you should consider getting your snake checked out by a specialist reptile vet.
Some of these vets recommend a shot of vitmain k to help tempt snakes to resume feeding but not being a veterinarian myself I cannot offer guidance on this subject.
Lastly, the cause may be none of these, and may be far harder to try and investigate.
For example, some snakes will routinely go off their food in both the summer and winter, feeding mainly in spring and fall.
It's natural and so long as you don't see any serious deterioration in their health is nothing to worry about.
You see, some snakes for no obvious reason will simply go off their food. They're fit and healthy and their care is suitable.
So what can you do? Here are a few tips that may help to coax a fasting pet snake back onto it's food. Remember to have patience and consider using more than one of these techniques in combination if at first you don't succeed.
1) Try a different food - if you're feeding mice try baby rats. Also try different sizes and colors (I have known people whose snake would eat only white mice but not black or brown colored ones).
2) Try warming up the food before feeding to make it seem like a recently dead carcass and / or consider gently slitting open the belly of the animal to allow more scent to radiate round the cage.
3) Try different light intensities. In general snakes seem happier to feed in subdued lighting or indeed total darkness that bright, glaring light.
4) Try adding one of the new liquids available which give off a strong smell of mouse or lizard to help tempt your snake to feed.
5) Rather than putting the food in the middle of the cage out in the open, try putting it somewhere more private - such as in an ice-cream tub with a hole cut in the lid for your snake to get through.
This extra "privacy" may be just what your need wants.
Lastly, if all else fails, remember to be patient and keep going. When your snake finally starts feeding again it'll all be worth it...