*cracks knuckles, stretches arms and dives in*
Here's part of my process:
My general approach is that the first time I visit a location, where I want to shoot birds, I look around to get a feel for what kind of trees/bushes grow in the area. Are there any traces of other animals? Can I hear/smell/see anything that gives indications of what types of birds to expect in that location? Even more than habitats suitable for nesting, I look for water in all forms nearby - water is crucial for all lifeforms, so it'll better be around!
Secondly I try to build a mental map of how the light and shadows behave, and I snap a few shots of the surroundings. At first visit I don't expect to bring home any superb bird shots. It's more of a reconnaissance.
When I go back to shoot "for real" I go handheld with a 400mm (and with a few other lenses in the backpack). The camera is set up for what I expect to find, and the lens prefocused to the distance at which I'm guessing I will most likely find my "prey".
Normally I don't use camouflage, but I do have a ghillie suit with me if needed. As much as possible I use the surroundings to my advantage, and I tend to not smell like a fresh rose... (The word "reek" should come to your mind.) The phone is on silent/vibration. I move slowly and patiently.
If there are any natural blinds, or birding towers, in the vicinity, I use them. What I see, I see with my naked eye or through my 400/5,6.
If I could afford it, my setup would be different, but I will have to cope with what I've got, and make the best out of it.
Whenever I can I try to pick up some usable knowledge from other birders and wildlife shooters (for example Brutus Östling -> http://cpn.canon-europe.com/content/ambassadors/brutus_ostling.do
And a final tip: If I get birds really close to me, I try to not be curious about them, but make them be curious about me.
What will get you closest to birds? If you grab a handful of seeds and chase around in a park, full of pigeons and sparrows, for 10 minutes, or you take the same handful of seeds and slowly walk into the park, opening the hand and then wait?