If you are using the content network, it is important to run a Placement Performance Report regularly. It will show you how your ads are performing on each site. If they don't do well on a site, add the url as a Negative Campaign Site.
Otherwise the general best practises are :
Keep your Content Network campaign separate from you search campaign.
Use more generic keywords than for search. It is important to realise that the ad will not be triggered by a specific keyword but by the adgroup theme, so stay granular.
In your ads, do not use keyword insertion.