A true keloid is very uncommon after surgery. On occasion, there can be a hypertrophic (thickened or slightly raised) scar.
My treatment usually begins prior to surgery, when I question the patient whether they have had problems with scars from major or even minor skin trauma (ie acne, insect bites, etc).
There is nothing that a surgeon can do during surgery to prevent a keloid or hypertrophic scar. (Obviously, I assume delicate tissue handling, accurate suturing of the wound and no infection.)
Once the wound is healed, very careful attention should be directed to it during the first few weeks after surgery. If there seems to be a propensity towards thickening, then there are a number of skin creams, such as Mederma and ScarGuard, which can help. Silicone gel sheets can also work, but they tend to be somewhat cumbersome. Finally, the surgeon can carefully inject some Kenalog or other cortisone into the scar to quiet it down.
The key is jumping on it quickly so that appropriate treatment can be initiated.
Dr Jacobs