Sounds like you're already part way there! Everyone has their own opinions on this, so this is my top ten:
1. Get the Haynes manual
2. Change the
every 9,000 miles and not the 18,000 recommended.
3. Use a petrol/ diesel flush quite regularly.
4. Always use genuine
5. Never use supermarket fuel.
6. Check steering and suspension components regularly by jacking up and giving a good pull and a tug. Common areas include rear bushes, suspension strut bearings, the dreaded ball joints, steering joints.
7. Inspect plugs every 9,000 miles - Just remember that these systems run at a very high voltage so disconnect the battery first.
8. Check all electrical systems regularly.
9. Look on here before going to a Renault dealer - there are often really good links/posts and how tos that show you how to do things cheaper.
10. If in doubt, ask!
A friend of mine who worked for Renault and subsequently Peugeot reckons that many problems with diesels in particular are caused by drivers not giving the car, in his words, 'The Governor' i.e. thrashing the pants off of it. He reckoned that half the problems he saw could have been solved with some occasional heavy foot and a good engine additive.