The most effective way of prolonging the life of your bolt cutters is not to use them to tackle materials that are harder than their recommended limit. For a general list of these limits by size, see: Which bolt cutters should you use for a particular job?
Other things you can do to maintain them are:
Keep joints clean and lubricated
Use a water-displacing lubricant spray to clean any grime from bolts and hinges and keep them moving freely.
Spray the solvent directly onto the bolt or hinge and let it soak in for a while.
Keep blades clean, sharpened and correctly adjusted
Use a firm bristle brush to remove any dirt or debris that may have gathered around the jaws. Wash them, if necessary, with soapy water, but make sure you dry them well or the metal may start to oxidise (particularly if they are an older model)
If your bolt cutter blades become dented or chipped during use, you will need to sharpen them to prevent the damage from getting worse.
It is also important to make sure your blades have the right sized gap between them. This prevents excessive pressure from being applied to the hinges while the tool is in use.
Long-armed bolt cutters should be stored upright – ideally hanging on, or fastened to, the wall. They need to be in an environment that is not damp, or their condition will deteriorate. Their hinges could corrode, making them stiff to use.
Compact
Compact bolt cutters are small enough to be stored away in a tool box. Take care to make sure that they do not get damp, as this may penetrate any scratches in the coating and lead to eventual corrosion.
If there is a catch to hold together the handles of your compact bolt cutters, it is worth using it as this also keeps the jaws together, preventing accidental damage from other heavy tools in the box.