Some links which are absolutely worth reading:
The rulebook - LRB6. This is roughly what BB2 is working to, although there are some changes. See "The NAF" link at the bottom for what it is thought those changes are. The NAF also provide lots of links to the rules including a number of clarifications.
BBTactics - not only a BB league in and of itself, but a great resource for articles such as cage breaking and how to beat Dwarves.
The Taouch! of Blood Bowl - great general strategy guide for newbies.
The Art of Blocking - assists, how they work, and how to set them up. PDF download.
Individual racial guides - includes roster tips and options.
One turn touchdowns - turn 16, you've just been scored against to make it 2-2 and your opponent thinks the draw is all you will manage? Time to think again...
Playbooks - a list of strategy guides for each race. Includes Bretonnians. NOTE: not all the teams or star players in these guides are available in BB2. Yet(?).
The NAF - The NAF is an organisation which is mainly tabletop oriented, but they obviously have an interest in online. The link includes a list of known discrepancies between online and CRP.
The 1000 Losses Playbook (PDF download) - the wisdom of a very experienced coach who not only has over 1000 losses to his name, but over 2500 wins.

Video:
cknoor's video guides - I'm told they are very good.

Math stuff:
Probability - a brief guide on probabilities and dice.
Samba Action Calculator - an awesome little tool from Elyoukey which can string together potential moves to see what the odds are. So when your opponent did that dodge, hand off, pass, scatter, catch and 2 GFIs into the endzone to win you can work out exactly how lucky he was. Because that's important!

Thanks dode. A compilation of must read for newbies and veterans.

The players who speak German, may also have a look here:

https://forums.focus-home.com/topic/448/beginners-guide-in-german-language-einsteiger-guide-auf-deutsch

He made a lot of different videos about the different aspects of Blood Bowl. (I didn't really watch them though)

A good and fun summary of match rules in 3 minutes: http://www.youtube.com/watch?v=TTLCjFq3mac

Fouling guides: http://www.thenaf.net/2014/05/putting-the-boot-in-revisited/
AND https://www.reddit.com/r/bloodbowl/comments/3nz9tl/the_complete_guide_to_fouling/

Interesting BB challenges/riddles (I guess some of them could already become a part of Challenges in LE): http://bbtactics.com/strategy/articles/challenges/ AND http://bb-oftl.blogspot.com/2013/01/blood-bowl-challenge-1-easy.html

Short descriptions of all skills in the game: http://coachchainsaw.blogspot.com.by/p/skills.html

Different block and injuries odds pre-calculated: http://bbtactics.com/blocking-statistics-odds-tables/ AND http://bbtactics.com/armor-break-and-injury-tables/

I also like this guy's team rosters and development guides, they are informative and fun : https://www.reddit.com/r/bloodbowl/comments/6orv09/lets_talk_about_kislev/ (check the list under the article, it contains links to other his guides)

Those are also good and cover vital core tactics:
http://bbtactics.com/marking-players/
http://bbtactics.com/cage-basics/
http://bbtactics.com/cage-breaking/

Most of those are covered in "The 1000 Losses Playbook", but I'm really not sure it's a good read for a newbie. Too much information he won't have a slightest clue how to apply, which will confuse him utterly and most of which will be most likely quickly forgotten. It's more something you should try to read after several months of MP experience, after learning the rulebook, reading about basic tactics/strategies and your first clumsy attempts to apply them in real matches, probably with not much success (at least it was like that for me )

You might want to post a link to this on the Steam forum too. There's a lot of new people making the same old beginner mistakes and complaints.

Best advice for rookie players is the game is about dice management. The goal is really to roll the dice as little as possible and only when u have skills and multiple dice to roll. On the other hand I want to make ur opponent roll the dice as much as possible. A lot of people say they have bad luck but in reality they are making a lot of rolls each turn based on bad positioning and eventually the odds catch up with u. U can play perfect and the dice give u the boot in the balls but the amount that happens can be greatly reduced

@dode74 Thanks for the link to helpful articles. I read them with pleasure now.