What should (not) a new bike rider do?

Hey all.

In a few weeks, I'll be moving to D08, though my work and schools are located in D02. I could use the bus, kr maybe even Luas, but I'm really considering starting using a bike. So, is there any "golden rule", tips and hints regarding the use of bikes and traffic rules (like extending your arm when making a turn)?

I wasn't sure about which tag to use, so I decided for "Irish culture". Thank you!