Factors influencing wound healing are the following:
Factors That Impair Tissue Repair 
Tissue repair may be impaired by a variety of factors that reduce the quality or adequacy of the reparative process. Factors that interfere with healing may be extrinsic (e.g., infection) or intrinsic to the injured tissue, and systemic or local:

Infection is one of the most important causes of delayed healing; it prolongs inflammation and potentially increases the local tissue injury.
Diabetes is a metabolic disease that compromises tissue repair for many reasons, and is an important systemic cause of abnormal wound healing.
Nutritional status has profound effects on repair; protein malnutrition and vitamin C deficiency, for example, inhibit collagen synthesis and retard healing.
Glucocorticoids (steroids) have well-documented anti-inflammatory effects, and their administration may result in weak scars because they inhibit TGF-β production and diminish fibrosis. In some instances, however, the anti-inflammatory effects of glucocorticoids are desirable. For example, in corneal infections, glucocorticoids may be prescribed (along with antibiotics) to reduce the likelihood of opacity due to collagen deposition.
Mechanical factors such as increased local pressure or torsion may cause wounds to pull apart (dehisce).
Poor perfusion, resulting either from arteriosclerosis and diabetes or from obstructed venous drainage (e.g., in varicose veins), also impairs healing.
Foreign bodies such as fragments of steel, glass, or even bone impede healing.
The type and extent of tissue injury affects subsequent repair. Complete restoration can occur only in tissues composed of cells capable of proliferating: even then, an extensive injury will probably result in incomplete tissue regeneration and at least partial loss of function. Injury to tissues composed of non-dividing cells must inevitably result in scarring; such is the case with healing of a myocardial infarct.
The location of the injury and the character of the tissue in which the injury occurs also are important.

    Robins 10 th ed page no 93
Nutrition
Adequate blood supply
Size and location of wound
All of the above