The only other thing I would add to GainfulShrimps advice about the slow lane is :
- Try and stay with the flow of traffic. When traffic flows at similar speeds it creates a 'down wind' effect which can help improve your economy. If you're overtaking people at quite a speed difference, or people are doing the same to you, you will see slight mpg drops on the instantaneous display. They are minor, but if you do a lot of motorway driving like me, it can add up over 700-800 miles per tank

Also, I do mostly motorway driving (I do around 30k a year and do 75-80% motorway), last summer I had a running average of 65mpg with a cruise speed of 70mph. I didn't see much of an mpg gain at all by dropping my speed to 60mph as I only saw a 1-2mpg increase per tank, because the fuel saving was negated by the need for more frequent regenerations. I'd prefer save time if the savings on fuel are that small!
This summer, with a looser engine, I expect it to be up nearer 70mph. I also do all of my driving withl a completely full, heavy boot full of tools/cables, with heavy parts on the back seat 1 or 2 times a week. In an empty car, at 70mph, I could be getting over 70mpg, and I believe that's because I don't baby the car in anyway
Couple what I've said with GainfulShrimp's advice and you should be set!
As an additional note, not sure whether you can do this, but I've seen most people on the internet who have it, reporting a 3-4 mpg increase per tank by getting the remap done. If you plan on keeping the car long enough, it will save you money in the long run. The nice side effect is you'll have smoother power, and more of it at around 135BHP.