Shimano's PD-M520 MTB SPD pedals are a great value entry level pedal that will give you great service with minimal fuss. They fit any standard pedal crank straightforwardly - just make sure, as ever, to put the correct pedal into each side...
Designed with mountain biking in mind, they actually suit any kind of cycling if you prefer the comfort and practicality of SPD cleats over SPD-SL road-specific cleats. The open design helps keep them clear of road muck and trail mud.
They're incredibly compact and lightweight, and having matching sides ensures you'll never need to twiddle them as you set off to find the 'correct' side to clip into!
These are durable, no-nonsense all-round pedals if you're either on a budget or just getting to grips with the joys (they really are joys, trust us!) of clipless pedals.