Part 1 of the Guide to Troubleshooting Your Skin: Know your skin type

The above chart has some great information, especially the care tips (click to enlarge).

1st: Know Your Skin Type

Most people have heard of the five common skin types: normal, dry, combination, oily, and sensitive. Generally, you can characterize a few common traits under each category.  

Normal Skin - your skin is not too dry or oily and requires minimal products to maintain its balance. Normal skin tends to have:

+ None to few blemishes
+ Is not sensitive to most products or potential irritants (e.g. fragrance)
+ None to few visible pores (skin has good elasticity) 
+ Even skintone and texture

Combination Skin - your skin experiences patches of dry, normal, oily, or sensitive areas, such as an oily T-zone (forehead, nose, and chin) but dry or normal cheeks.  Your skincare routine typically requires different products for different concerns on your skin.  Some traits found in combination skin types include:

+ Uneven skintone and texture 
+ Dilated pores
+ Oily T-Zone and dry/normal cheeks 
+ Blemishes (eg. comedones, acne, redness)

Dry Skin - your skin can be especially suspetible to seasonal weather changes and the skin can crack, peel, and become itchy, inflamed, or irritated.  Sometimes dry skin feels rough to the touch and produces flaking when make up is applied.  Dry skin can include: 

+ Red, rough, or scaly patches
+ Reduced skin elasticity
+ Dry wrinkles or lines
+ Dull and uneven skintone
+ Little to no visible pores 

Dry skin can be cause by or made worse by the following factors:

+ Genes
+ Aging or hormonal fluctuations
+ Weather
+ UV exposure
+ Excessive indoor heating or cooling (e.g. sitting in an air conditioned office all day)
+ Long baths and showers
+ Irritants in cosmetics and soaps
+ Nutrition
+ Exercise
+ Medication

Oily Skin - your skin is shiny and can produce that "slick" feeling throughout the day.  You may be susceptible to weather changes, especially when warmer, more humid seasons start causing you to notice an increase in oil production.  Oily skin typically includes: 

+ Overly dilated pores
+ Uneven skintone that can be dull or shiny
+ Blemishes and clogged pores (e.g. comedomes, acne, large blackheads, etc.)

Oily skin can be caused by a variety of factors, most commonly: 

+ Puberty or hormonal imbalances (mentrual cycle changes)
+ Stress
+ Weather changes (e.g. too much heat or humidity)
+ Heavy persipiration after exercising
+ Harsh and overly drying cosmetic or skincare products, including potential irritants

Sensitive Skin - your skin may react negatively to products with fragrance, alcohol, or other potentially irritating ingredients.  Sensitive skin can include:   

+ Redness
+ Itching
+ Inflammation
+ Dryness
+ Uneven skintone
+ Burning

Sensitive skin typically has several chemical and ingredient triggers which can be avoided if you know what your skin reacts to.  However, this can be a trial and error process where you won't know what to avoid until you've had a flare up or negative reaction. There are certain groups of ingredients that someone with this skintype may want to avoid in general, such as any products with high alcohol content, limonene, fragrance, or dyes, etc.