I put together this tutorial a while back for beginners who are making small games, but it contains some useful general advice:
In addition to that I would recommend the following:
1) Organise your project folder system to make it easier to manage assets. I use the following "ABCD" folder structure:
Keep archive subfolders so that you can declutter old unused files from your main folders.
2) Use a naming convention for your assets. My preference is (assetType)_assetName_(indexNo) e.g.:
...but exactly how you go about this is up to you. The main goal is to make it easy to organise and identify assets.
3) Learn how to use groups, functions, families, arrays and dictionaries. Whilst seemingly daunting at first, these objects and structures in combination can go a million miles towards improving the efficiency and versatility of your code, and actually aren't that hard to get to grips with once you start playing around with them.
4) Use the manual, tutorials and forums, preferably in that order, whenever you get stuck. Whilst it can be fun to noodle over a problem you can often waste a lot of time reinventing the wheel; if you can't find a solution and post a question provide as much info as possible - capx/c3p files are always appreciated.
5) Start small - try not to bite off more than you can chew for your first few games. You'll learn more and progress faster seeing a number of simpler projects through to completion than if you get bogged down creating your magnum opus. Have a look at the example projects that come bundled with C2 and try modifying those into a game - this is a great way to familiarise yourself with many of the different plugins and behaviours that C2 offers.
There's plenty more I can add on but I reckon that's enough to kick you off - Hope it's useful -