I'm working recently on many TYPO3 Projects and I'd like to have a good tutorial/reference to work my way up. I'm looking for something like Agile Web Development with Rails but for TYPO3 if you like. The documentation of TYPO3 is good but not incredible so I was wondering if there was a better option out there.

Unfortunately there aren't a whole lot of TYPO3 books available; the only publisher I know of who have put any effort into them is Packt, who have a few:

• 
  Building Websites with TYPO3


• TYPO3: Enterprise Content Management


• Mastering TypoScript

Amazon

• TYPO3 Extbase: Modern Extension Development for TYPO3 CMS with Extbase & Fluid

I don't own them so I can't testify to their quality, unfortunately. But since they're the only game in town I suppose that doesn't really matter that much :-D

Generally speaking, the best resource for learning TYPO3 outside the documentation is probably the TYPO3 mailing lists; I often find answers to questions just by searching the archives. TYPO3-English is for English-speaking general users; TYPO3-dev is for extension developers and those who want to hack on TYPO3 itself.

I would advice also of Patrick Lobacher "Certified TYPO3 Integrator" (English edition, e-book-version).

There are lots of examples with detailed explications, and this book will help a lot, if You would like to pass TYPO3 certification.

https://www.opensourcepress.de/index.php?26&tt_products=294

Agree with jalefkowit - the Packt books are an excellent reference. I use my copy of Typo3 Enterprise Contente Management regularly. The mailing list is truly staggering in terms of what's in there. You can find answers to most difficulties in there somewhere.

A key thing I've found is spending time getting to know the api well. A good technique is to look for an extension that does something similar to what you want and then pull it apart to find which api calls it makes. You can then use the api browser to find out how it links to other objects - see api. typo3.org

Also very useful in terms of general strategy are
the English translations of the T3 magazine articles
typo3.org/ documentation/t3n-magazine/
working your way through the many excellent podcasts
typo3.org/ podcasts/kasper
Dimitry Deulpov's blog has some brilliant insights
dmitry-dulepov.com/ category/typo3.html

Good luck - sorry for weird links - only allowed 1 link as a newbie

There are quite some video tutorial available on https://www.youtube.com/user/typo3/videos
Each Friday a new video is published, so the channel is worth subscribing. On the same channel you will also find recordings from TYPO3 conferences where they go deeper into certain topics.

Some of the answers here are quite outdated, so I would like to provide a new answer.

For getting help in general

• 
  Register and join TYPO3's Slack Platform and ask in the #typo3-cms channel. You can also use #typo3-documentation to ask about documentation.

It is always a good idea to ask on Slack about where to find help for your specific task, because it depends on what you plan to do and on what level you are on. Are you for example a complete TYPO3 newbie but a very good programmer? In that case, you need different information from someone who is already familiar with TYPO3 but will start from scratch as a programmer.

In some cases, an official TYPO3 YouTube video is a better fit to get started. There is not a one guide or book for TYPO3 developers where you will find it all.

For extension development

print

• Schams / Lobacher: "TYPO3 Extbase: Modern Extension Development for TYPO3 CMS with Extbase & Fluid"

official documenation

• 
  Site Package Tutorial : Shows how to create a "Site package" extension. This is what you would in other contexts call a "theme" extension or "template" extension.


• Developing TYPO3 Extensions with Extbase and Fluid


• 
  TYPO3 Core API - For developers and people who want to understand TYPO3 under the hood. It is announced as a reference, but it is actually a good read and quite up-to-date.

In general, for official documentation, go to https://docs.typo3.org/ and look at the pages "References" and "Guides and Tutorials". The tutorials are best suited to get started.

You should select the correct version of TYPO3 you will be using. By default, the "latest" version is loaded. "Latest" is the latest development version, it may not be the latest LTS. Click on "Related Links" (usually in the bottom left) and select the version.

In addition I would like to recommend the TYPO3 Extbase/Fluid Cheat Sheet. It has been a great help to get an overview of all the most important classes, structures and viewhelpers in Extbase and Fluid, and also as a quick reference. It's a bit outdated by now, but still very useful.