What is the best way to treat acne scars?

The treatment of acne scars depends on the type of scarring it is. Typically, when a patient presents to me with acne scarring, I will treat each scar individually as required, and then consider fractional laser for the involved areas. The treatments of each indivicual scar depends on the type of scar and other features of the scar including width and depth of the scar, and what the edges are like.
My favourite treatment for suitable acne scarring is dermal fillers, especially hyaluronic acids, which include Restylane, Perlane orJuvederm. Patients LOVE this treatment as it takes about 30 minutes and gives an obvious instantaneous result.
My second favourite treatment for acne scarring is ablative fractional laser, where the laser causes hundreds of “pin holes” in the skin and new skin regrows. This only treats about 10% of the surface area of the skin, so multiple treatments are necessary to get decent results. I recommend a minimum of 5 treatments of fractional laser.
Other treatments I use for acne scars include subcision, punch biopsy, punch grafting and ablative laser.
If the scars are keloid then treatments might include silicon gel sheeting and intralesional steroid injection. 
A factor that is often overlooked in the management of acne scarring, is that acne scarring often gets worse with aging. The main reason for this is due to volume loss, so it is extremely important, as the patient ages, to keep on top of their facial volume. There are many fillers which are great for this, including Restylane SubQ, Perlane, Radiesse, Sculptra and Modelis.

Further to this topic, of acne scarring,  often patients come into my clinic with what they call “acne scarring”, which is not in fact acne scarring, but a pigmentation issue associated with acne which is quite disfiguring.
It is called post-inflammatory pigmentation, which appears as brown spots at the site of the pimples. It is caused by combination of factors including inflammation and skin type (those with darker skin tones have a higher risk for developing PIH).
Treatment I recommend for PIH related to acne is a combination of bleaching agents (eg hydroquinone and kojic acid) and tretinoin (prescription Vitamin A). Topicals are the gold standard for treatment of PIH. If left untreated, PIH will usually go away, but may take a long time (up to 18 months) to go away.

1) Fractional laser  Skin Resurfacing and

2) Medical grade Skin Needling

are two good treatment options for improving true acne scars permanantly. Both procedures work by stimulating collagen production and breaking fibrous tissue adhisions to an extent.

Multiple treatments are required over several months for optimum results.

Naomi and Ehsan are right on the money here!

I might do more subcision and eDermastamping than most, but otherwise we all agree on the best approach here for acne scars.

Acne scars are often an unwanted reminder of those earlier days with active acne lesions. The first thing I recommend is to treat any ongoing active acne to prevent more scarring.

In patients with darker skin, resolved acne lesions often leave behind darker patches called post-inflammatory hyperpigmentation that can be lighten with prescription bleaching cream and medical grade skincare products.

Cortisone injections can help flatten any hypertrophic or keloid scarring, and the red component can be lessened with intense pulse light or laser.

The most common acne scarring is the atropic or ‘sunken’ scars which can appear worse with ageing as the face loses subcutaneous fat and becomes more hollow. The gold standard treatment of atrophic acne scars is a series of ablative fractional resurfacing laser treatments that can lead to over 50% improvement in the scars over time by stimulating collagen regrowth in the scarred areas.

Hyaluronic acid dermal fillers can also be injected to plump up the atrophic scars for those not keen on the downtime and expense of laser, or to improve residual scars left after laser treatments. Results are immediate and downtime is minimal.