My 1st generation 15" rMBP is getting close to its 3rd year. The original owner bought it in August 2012 and I bought it off him in March 2013. The screen coating is as good as the day I got it. From the onset, I made sure I don't use any solvent- no alcohol or ammonia based window/glass cleaner like Windex. Only water and old, worn, super soft but clean 100% cotton t-shirt (like my 5 year old American Apparel white t-shirt).

I know a lot of people go overboard when cleaning the screen. Either driven by OCD, you tend to clean it too often, putting way too much elbow grease and constant use of solvent. At the other end are those who let their laptops get covered in dirt and grime, thus, when they do decide to clean it, it's easy to do too much because that's the required effort.

What I would do is make sure after each use or every night, give your laptop a light wipe or dusting- eg. using a Swifter duster (use the 360º duster instead of the single-sided as it would minimise accidental scraping). If you don't have an old, soft cotton white t-shirt, use a good light colored micro-fibre cloth. Why white or light colored? To easily detect sand or dirt.