Succulents are well-adapted to the conditions of the biome that they generally come from:  Deserts.

Light

Lighting ranges from direct sun, bright light, filtered-bright light, to medium light.

The succulent's size, leaf/stem color, and texture are good metrics for suitable light levels.  Succulents may be grown indoors and outdoors, though the majority have a predilection toward the outdoors.  A reliable guideline to go by is that green leafed/stemmed succulents can tolerate less light than tinted (e.g. black or red colored succulents) / textured (e.g. succulents with sheaths or hairy coverings) varieties.

Lighting Indicators

Insufficient Lighting

  • Etiolation - Some succulent varieties, especially echeverias, are known to "etiolate"/elongate as if to "reach" for a better light source when there is insufficient light.
  • Lightening - Plant leaves will discolor to lighter shades of green and eventually turn yellow (then brown ...then fall off) if left without sufficient exposure to light wavelengths.

Excessive Lighting

  • Burns & Callousing - Many like cacti and echeverias result in a woody callous where sunburned.  Thinner plant tissue will be more susceptible to burning so exercise caution as to where you place your plant.
  • Darkening - Varieties such as Haworthias and "Flapjacks" can deeply discolor to a reddish tinge to show signs of sun stress.  Sun stress can be ok if the plant doesn't begin to dry out.  In fact, sun stress gives many succulents their character.

Soil

Many succulents grow in rocky/gritty mediums with little soil organic matter.

A balanced soil mix that considers aeration, moisture/nutrient retention, and compaction prevention is advised.  Ensure that the pot/vessel has excellent drainage to prevent water from collecting at the base of the pot, which would thus result in rot.

Water

Water succulents thoroughly (until water runs out of the drainage hole of the vessel) when the soil medium dries out.  Do not water again until dry.

Most succulents thrive, believe it or not, when left dry for prolonged periods of up to two weeks or so.  The succulent's soil/medium, current weather conditions, and plant warning signs may, though unlikely, override the general 'wait until dry' re-watering rule.  It's best to water succulents as necessary as opposed to a set schedule as each individual plant's needs will vary.
NOTE: Ensure that the plant does NOT reach "bone dry" status, however, as this compacts the plant's root system and consequently compromises the plants' ability to absorb water.

Watering Indicators

Overwatering

  • Stems/Leaves are tender or excessively plump to the point of ease in rupturing plant tissue.
  • Stem/Leaves start to discolor dark brown/black and plant base is flimsy.  Leaves toward new growth fall off with a slight touch.  This is a sign of rot and usually signifies a dead plant.

Underwatering

  • Leaves toward the base of the succulent fall off more easily than usual.
  • Stems/Leaves are shriveling rapidly.  This is especially alarming if shriveling occurs near the growth point at the plant's center or top.  However, this can be rectified with thorough watering.

Tillandsias come from humid regions.  They receive their sustenance by absorbing moisture that carries microscopic nutrients from decaying matter.  For this reason, air plants such as Spanish Moss and Xerographicas thrive without the need for a soil medium.  

As with other plants, care factors for Tillandsias vary by geographic region of origin and plant type.  Tillandsias come in two flavors: Mesic and Xeric.  Mesic airplants (tillandsias with smoother leaves) hail from regions with more frequent moisture whereas xeric types (air plants with more white hairs/'trichomes') are accustomed to the arid conditions that they're native to.

Light

Full spectrum bright, filtered light for about 12 hours.  Direct morning light makes for happy air plants.

Tillandsias may be grown indoors or outdoors as long as they receive light.  If an air plant lacks sufficient light, the plant will shut down and will fail to absorb any nutrients from watering (which will consequently result in rot).

Be sure that tillandsias aren't exposed to direct noon/afternoon light as this will scorch the leaves.

When growing indoors, be sure that the air plants are situated no more than 10 feet away from a window/full spectrum light source.

Water

Depending on weather, generally mist once every other morning.  If leaves curl to indicate dryness, an optional thorough wetting for 5-10 minutes once every week or two may be needed.  

Mesic types require thorough saturation every 3-5 days.  Xeric tillandsias may be wet thoroughly every 7-10 days.
Flip Tillandsias upside down after misting/soaking (see Air requirements).  Allow Tillandsias to dry within 4 hours after watering.

Air

Air circulation is necessary for rearing healthy air plants.  Keep a window open around air plants if indoors.

Bearing in mind that Tillandsias receive sustenance from constant moisture powered by air movement, these plants thrive from constant and fresh moving air.  

Mold results from Tillandsias kept wet or have had water sitting within the leaves for too long.

Soil

None needed.

Keeping air plants in soil actually encourages mold growth.  Tillandsias may be mounted on dry, non-porous surfaces.  If mounted on porous surfaces, be sure to remove plant from surface before watering and replace plant on surface after completely drying.