I think a big thing is how old you are. I swear there is a direct correlation to being older and having more success in tight brush. My grandfather, 80+ and father 50+ are perfect examples. You know what? I am getting better in the brush, what does that tell you?

I watched my Grandpa in a spotting scope walk the side of a hill one time and he came within 50 yards of 7 bucks. The only problem was that his eyesight was gone and he couldn't see them.

He didn't even believe me, or maybe didn't want to believe me, when I told him. I love watching folks walk through the brush with a spotting scope. The animals are long gone and bucks literally run circles around them. Brush busting and walking isn't what you want to do. Watch a buck, if you can, outside of the rut, in August or early October. Sometimes it will take them a half hour to walk 20 feet! Simply, that is what you have to do to be successful.
Go slow and even that is too fast. The trick that I use, that came from an uncle, is to walk the width of a road in 15 minutes. If you can do that you will start seeing deer. Believe me, it is tough to stay that focused when you want to look into the next draw or you see a "good spot" or you are entirely sure that there are no deer in the area but you have to do it and you have to stay with it.
I like hitting the brush in a big wind storm after a good rain. Usually after a cold front comes through and it rains a wind storm is on the tail end. When the wind is blowing 20+ mph I love it. Now, the deer are spooky and they are holed up in the tight brush but things are falling off the trees, the trees are moving and there is a whole lot of movement and sound in the forest and that covers me up and it also makes scent a non-issue because after a cold front it doesn't swirl. It evens the score, their ears are as good as mine and there nose is taken away, that only leaves sight to their advantage (which is still a big advantage). You have to move like I said above, 15 minuets for 30 feet and use your glass and you will still spoke them every-once-in-awhile but it sure is fun.