The main Lighting page explains the game's lighting mechanics in great detail. This tutorial is mainly concerned with lighting designs and aesthetics.
Lighting section headings
Concealed lighting
While rows of torches can produce quite a homely feel, sometimes one wants the light sources not to be apparent. The simplest way to do this is to hide the light source behind a transparent block other than glass. Pistons are a common choice for this trick, but there are many other options, including leaves, fences, walls, stairs, ices and so forth, depending on the lighting style desired.
Minimum lighting
Minimum possible lighting.
With torches, the minimum possible torch pattern that prevents mob spawning is to place torches in a diamond pattern with a five block diagonal gap between torches. Note that this is only reliable on completely flat ground; on rougher ground, torches need to be closer or there will still be some dark spots where mobs can spawn.
Preventing mob spawning
There are two main ways to prevent mob spawning. Adequate lighting is the most obvious method, but another alternative is to ensure they have no valid spawning spots. This trick is of particular interest when designing lighting, because it allows you to have very low light levels without any risk of mobs appearing. The most common way to achieve this is to use a slab floor, as mobs can only spawn on opaque blocks where there is sufficient headroom.
torch
villager wool block
fence posts + lamp
iron railing chandelier
walls/floors of light fence post combos steps+ lamps fire lava lava behind iron/glass braziers