A collection of articles aimed at newer 40K players, but perhaps with value to some vets as well:
40K 6th Edition Impressions series:
Part 1 - Intro
Part 2 - Special rules
Part 3 - Unit types and weapons
Part 4 - Characters and psykers
Part 5 - Vehicles
Part 6 - Terrain
Part 7 - FOC Allies Warlords and Fortifications
Part 8 - Missions
Part 9 - Wrap up
Example 5th vs. 6th editions battle report
How to Make Stuff Work
Simple Numbers
Objective Placement
Pick up Games
Are you using everything in your toolbox?
Wound Allocation (5th edition)
Casualty Removal (5th edition)
Damaging Vehicles flow from Wargaming Tradecraft (5th edition)