You can't do much with deserts in the early game. Irrigation only makes them support one more population, roads add one trade, mining adds a shield. Mining isn't worth the settler turns (make a new city instead), irrigation also takes a long time for little gain (make a new city instead) and roads only help in areas your cities are working (or troops travel frequently).
You have three options for city building. Build on the oasis and work desert, build on the desert and work oasis, or find a spot with better terrain. The first two options give 3 food, 2 shields, 1 trade. Option 2 potentially lets you work more than one special (though ICS should fill up those special squares quickly). Option 3 is superior if you have any choice (nearly anything is better than desert). If you haven't studied ICS yet, now is a good time to start. Very small cities (pacified by Hanging Gardens, once you get enough of them) need only a few workable squares each, and you get free irrigation/mining/roads and a bonus worked square for each city center.