Petrol or Electric?
Electric mowers are good for small gardens, but the cable limits their range. Serious lawnmowers tend to powered by fuel.
Horses for courses
Both of the main types of mowers (cylinder and rotary) are made as petrol-driven and electricity-driven models. Petrol-driven mowers are generally bigger and more robust. Electric mowers tend to be lighter and more manoeuvrable, and less noisy, but being attached to a powerpoint by a cable is both a restriction and a hazard. In general, larger gardens are best served by petrol-driven mowers, while small gardens are best served by an electric mower - or even a hand-propelled cylinder mower.
Getting the thing started
It's easy with an electric mower: you just plug in and switch on - usually using two starting triggers (e.g. a button and a lever) for safety. Petrol-driven mowers can be more difficult. Some are fitted with a manual pull crank (or recoil start), which involves heaving at a cord - and sometimes battling with a general reluctance to function. Others have an electric key start system, but these models tend to be more expensive.
Petrol engine maintenance
You should consider changing the oil once or twice a year, and replacing the spark plug and air filter. Note that new machines tend to run much more cleanly than old machines.
Two stroke/four stroke
Many of the older petrol-driven mowers had two-stroke engines. They were cheaper to produce because they had no valves, but they needed oil in the petrol mix because the engine did not have a separate oil system (unlike a four-stroke engine). Modern petrol-driven mowers have four-stroke engines, which are both cleaner and quieter, and run on unleaded petrol. If you run a two-stroke mower, you can buy special oil additives to mix with standard petrol.
Circuit breaker
When using an electric mower powered by mains electricity, be sure always to use a circuit breaker, or 'residual current device' (RCD). This will immediately shut off the power, should you accidentally slice through the cable.
Cordless electric
Some electric mowers are cordless: they are powered by rechargeable batteries. This means that you don't have to cope with a long, trailing electric cord. But the charge will give you only 30-75 minutes running time, before the batteries will need recharging, a process that takes between six and twenty-four hours.