What is the best pre- and post-care for the Halo laser ?

Your doctor will give you a comprehensive list but the most important basics are to avoid any UV light for 48 hours. Then after 48 hours to apply a physical based sunscreen 2-4x/day (whenever you are getting any indirect light) for the next 2-3 weeks. 
The other critical post care is to keep the skin hydrated but let it breath. A non occlusive hypoallergenic moisturizing cream like Cetaphil is the safest and simplest option. Keep it in the refrigerator as this will feel nicer when you apply it. After day 2-3 (depending on your rate of recovery) I like the Keracell MD facial moisturizing cream and Under Eye Contour Lift cream to support hydration and healing. 
There is a hypoallergenic preservative free stem cell based serum that has consistently proven to be safe in my practice that I think significantly improves results and shortens healing time called Keracell MD Recuperate (MD is essential since the non MD version has preservatives that may aggravate healing skin) use this 3-4x/day from day 0-6 immediately after cleaning the skin and before applying moisturizer. 
The other product that I think significantly improves healing and results is Acuicyn spray. It is meant to clean eyes but it is a hypochlorous acid that forms a film on the skin and contains Oxygen that helps with wound repair. It is a gentle as Saline and as potent as bleach and it is the same active ingredient that your White Blood Cells use to kill bacteria, yeast and viruses. 
Every time you remove the Cetaphil (by gently patting, never scrubbing, with a cold water soaked wash cloth) you should apply 3-5 sprays of Acuicyn, then let it dry and apply the Keracell MD Recuperate, then apply the Cetaphil as a thick layer. Once the skin is no longer red and raw (day 2-3 usually) then you will use either a light coat of Cetaphil or the Keracell MD moisturizer followed by Elta MD UV Physical (only zinc oxide and titanium dioxide) Tinted sunscreen. You will repeat 3-6 x/day as needed when your skin starts to dry out or you need more sunscreen (one application is good for 2-3hours). Wear hats and sunglasses and stay out of the direct sun as much as possible for the first month and avoid prolonged exposure to indirect sun in the first 2-3 weeks. 
No other beauty products should be used for the first 48 hours (None!). Makeup can be used on day 3. I like RMS beauty since it is a much cleaner make up line. Sephora is a toxic supermarket so steer clear pretty much everything in there except the Elta MD physical Sunscreen. 
Benadryl at night and Allegra during the day can help reduce swelling. Avoid hot water to the face or exercise to reduce swelling or irritation to the skin. Sleep propped up to avoid increasing swelling under the eyes. Drink plenty of water. 
Consider these supplements: 
Perque Potent C Guard 3grams 2x/day, 
Douglas Labs -Joint Tendon Ligament I 3 tab/day  
Mitocore by Orthomolecular 2 tab 2x/day 
Working with a functional medicine doctor can address deeper issues that support healing that require more nuance such as digestive, hormonal and nutritional health.