Web Resources

Online Autodesk Resources 

Autodesk Forums
http://forums.autodesk.com/
Create an account and post your question or answer other people’s questions when you have the answer. Before you post though, make sure someone hasn't already asked your question. This will get you to the answer sooner!

Autodesk 360
https://360.autodesk.com/
This is Autodesk’s cloud service, which allows you to load cad files to the cloud, and share them with other people for editing. You can use it to upload files to view on a different device when you're out in the field.

Online Resources

CAD Blogs

AutoCAD Official Blog
Reference

LinkedIn Articles
Reference

Lynn Allen's Tips and Tricks
Reference

CAD Details Blog
https://caddetailsblog.com

CAD Intentions
http://cadintentions.com/

Civil 3D Plus
Reference

CAD Forum
http://www.cadforum.cz/cadforum_en/default.asp
Here you can see other people's questions and they also have a library of AutoCAD commands, which are often explained in greater depth than the help files. They also have a AutoCAD block user library. There are some great blocks for steel beams and other structural features. 

Manufacturers’ websites

You can often find CAD details online that you can download into your drawings.
Skyline Steel: Sheet pile
http://www.skylinesteel.com/globalnav/technical-library/datasheets--autocads

United States National CAD Standard
http://www.usbr.gov/foia/Vol%20III/NCS-CAD_Layer_Guidelines.pdf
You should also check DOT and engineering company websites in the state you are working in for CAD standards.

Details

ARCAT
www.arcat.com
Free details and specifications and no registration required.