I never read the book by David Allen. I just read about the method here and there and put together my own method, which might resemble the "official" method more or less -- I don't know. What I did gather was that the book opened many eyes and introduced a solid structure and a vocabulary when discussing workflows and systems for getting things done.
But I realized over time though was that the key to get things done is not listing all the tasks you should but keeping track of what you have accomplished. It sounds like semantics but it has a high psychological impact.
They key is not too overload yourself.
When I first started with GTD I found myself overloading with tasks. When you find yourself in the same trap, step back and review your tasks. In my work environment I find it best when I just tackle one to three problems (read bugs, features, meetings, ...) at most a day. If you can finish all of them, start the review process again and pick another task to spent time on. It seems lazy at first, but try it out and you might find yourself even more productive. For me it surely increases the quality of my work and the pleasure.
Keep that in mind. Don't let the process define your workflow.
I always keep pen and paper at arms length and even if I'm out and about I still keep a small notebook in my pocket.
When I'm on my Mac I always use The Hit List to write down small tasks as soon as the enter my mind and can't be done right now. More complicated stuff I commit to my notebook first for reviewing it later.
I think this step is the most important one. Everyone should have a good way of collecting tasks as there are so many different sources where ideas can be spawned (emails, calls, co-workers, friends, meetings, your brain) and each has to be handled differently.
I constantly get emails and tend to get wrapped up in them. Even worse you can get wrapped up in letting the incoming flux of emails define your workflow by constantly reacting to fresh emails. Emails almost never contain urgent tasks, so it doesn't hurt to let them wait for a few hours. I try to only fetch them two or three times a day, which in all honesty almost never works, but I have to try.
I follow the empty inbox routine and try to have my inbox empty at the end of the day. When working through the emails, I make use off all the organizing features my offline client has to offer. I have a rather rigorous hierarchical structure. It's based on my needs and basically sorted after the clients and projects I work for. (On a sidenote: Use IMAP and ditch POP3.) Currently I employ 30 or so filtering rules that sort most of my mails into specific folders. For all my manual sorting needs I use MsgFiler, which enables you to store away emails only using the keyboard (For Thunderbird there is Quickfile).
As the filters move away some emails automatically the inbox and I store all email in meaningful directories, the inbox gets its meaning back. It's an inbox. It should be tended to and emptied.
So when starting the mail client I normally don't access the inbox but a smart folder called @unread, listing all unread emails.
First I do a rather quick review and mark (by pressing Shift + Cmd +l) all mail that should get my attention (today). This is often necessary as most of my emails are just noise (Notifications from Ticket System or Versioning Systems and chatter from projects I'm not fully involved at the moment, but for which people put me in CC, and so on). Then I go back to my inbox and sort away the mails that couldn't be matched by filtering rules. Luckily I can setup rules in such a way, that only few get trough.
Next, I use a @action smart folder to show just marked emails. I tend to use this as my main todo list, although I keep my own GTD application (The Hit List) running in the background. I do this because I have to keep track of all tasks in our company wide project management application (Redmine) that sends my notes about new tasks for me in any way. I do keep my application running though for project planning purposes or if I a personal todo item should come up in the course of the day.
Try to treat it like you treat emails.
I had positive experiences with it. I worked at a company that used an internal jabber based instant messaging service for support services.But in general it doesn't serves my needs. If its urgent, call, if not email the person.
In general I don't like calls as they interrupt your normal self-directed workflow. They seldom can't be planned, need to be answered right now and normally include a call to action.
Mainly because of calls I still depend on good old pen and paper right beside my keyboard for writing down things. Normally you discuss things on the telephone you can't break into actionable items without reflecting on them. So I just use my pen to write down the time of the call and the gist of the content. Depending on the content of the call I work through it right after I hung up or make actionable items out of it When I hung up I react on it. I work through the notes and by delegating it to someone else, marking it as a thing to review later, creating a bug report right now, or something else.
It sounds strange but If a colleague has a question, they normally don't get my attention right away, at least not always. Thats somewhat because of my line of work. When you do software development, you often find yourself in deep concentration. I know it sounds harsh but if you do have a problem, do your own research first. Maybe it has a simple solution. Only if you know your problem approach the guy who you suppose has an answer to it, but be so considerate to ask if he has the time for you if its a bigger issue. Chances are if its a bigger a problem, I also want to solve it, as I might run into it. I always try to free up some time as quickly as I can.
If you have other tasks you can do in the meantime just ask them for 10 minutes and ask them to approach you If they do have the time. As with telephone calls, using a PC isn't as expressive and fast as pen and paper. It is better to just use a trusty pencil if you have to communicate ideas and record actions that present yourself during the exchange.
Of course there are exceptions to this rule. If it is really important, make your point clear. If a production server is down and clients can't use some service, don't wait half a day until the administrator has time for you.
Sometimes you don't have a specific problem, but a rather fuzzy problem, maybe a design decision or you need someone to bounce ideas to and from. Just ask for the time and have a go at that whiteboard.
In short: I like short, informal, standup meetings. But even if it is formal I just use a pen to collect the information I need from it.
I try to schedule a weekly review sunday evening to work through my tasks that don't have a scheduled date yet. These tasks are often ideas for other projects that just wait to be done and are seldom tasks that have to be done for work. Often I find myself missing that weekly review as I'm still held up in current tasks. I want to try to this more often as I think that this weekly review process is also helping me in a way to prioritize the things I like and love which in turn hopefully helps me to lead a better life. For work I find that tasks have a lower half life, which don't need to be reviewed in a weekly process.