Here's a quick table summarising the basics of solar systems in Elite: Dangerous.
To make a fast buck exploring:
1) Jump to a new system.
2) Perform a system scan.
3a) Scan the star.
3b) See if there are any small planets really close to the star. These are good because they are likely to be metal-rich or at least high-metal-content, and because you can probably scan them without having to move your ship. Do so.
See if there are any gas giants close enough to scan (generally under 800ls), especially if they are white Class II gas giants. Do so.
You may also spot Water Worlds, Earth-Like Worlds and Ammonia Worlds, White Dwarfs, Neutron Stars and Black Holes; these are always worth a detour to scan.
3c) Look at the type of star. Look at the habitable zone on the table. If there are small planets of the right type (HMC, WW, Rocky) on the scan around that distance from the star (1AU is about 500ls), they are possible Candidates for Terraforming, which is where the money is.
Go and scan planets in that zone. If the surface temperature is really high and they are not a Candidate for Terraforming, scan the next planet in. If it's really low, scan the next planet out. You'll get the hang of it once you start finding them.
That's it, really. Jump in, see if there's anything you can grab easily, see if there's anything cool like an Earth-Like world, look at what distance the habitable zone will be and scan any suitable worlds near there, move on. If you jump to a system full of rubbish ice worlds, jump on until you find a system that's got good stuff.
