Supply Ship Smash and Grab

Supply ships en route established alien base may offer an extremely easy way to earn both elerium and money. Letting the right alien base live, rather then storming it, will result in a steady elerium supply ranging from 150 to 900 elerium/month, and some money.

Race considerations

Floaters are best due to their generally crap stats. Next choice would be Snakemen, then Mutons. Sectoids are dangerous due to the Psionic Sectoid Leader in the bridge if you have not psi-screened your squad yet (though this is a common way to nab a Sectoid Leader if you need one). Ethereals are in general far too dangerous unless your squad is entirely psi-immune.

Terrain considerations

The best choices are flat and level deserts and arctic terrain. Farms are acceptable, though you'll have to deal with the barns and stables. Jungles, forests and mountains are to be avoided.

Know the different appearance of sub types of terrains. Deserts may be flat or hilly. Arctic terrain may be solid or puddly:

Unless you have flying suits, the puddly ice may present serious obstacles.

In farm terrain, remember that opening unexpected holes in buildings can be advantageous, and remember to check orchards thoroughly.