Basic GTD: What does collecting mean?
It is the first stage through which any possible action or task has to pass. First of all you have to catch it. Collecting is to capture everything that might represent something you have to do into a reliable system you will process and review later. So simple: noting down something in your notebook, recording a thought in a voice memo, entering a task in your favorite application…
The difficulty is that, to be efficient, you must collect everything. If you do a halfway job, there will always be things in your head distracting you and, moreover, you won’t review the collection system as often as you should, because, deep down, you won’t trust it.
Try to use the minimum number of collection tools. If you have to watch your 3 email accounts, your mobile phone, your notebook, an Excel spreadsheet, the application you use at work and the one you use at home, believe me, you will end up forsaking.