Follow the diameterX2 rule about clearing out around your most promising trees. Take the tree measurement at breast height in inches, change that number to feet and take it times two. This should be your spacing between trees. For example - if you have a nice white oak measured 10 inches at breast height, then change the 10 inches to 10 feet and take that times two. Spacing between trees should be 20 feet. Getting your most promising trees ample sunlight will be a great help.
Here is a link to a pretty good brochure on TSI - http://mdc4.mdc.mo.gov/Documents/285.pdf
We don't fertilize, I've heard arguments both for and against, and can't say one way or another if it helps.
We're putting in an orchard, but right now all we've got is a lot of trees poking out the top of tree tubes. I do recommend tubing trees if you're planting them, it keeps them safe from deer.
“There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery, and the other that heat comes from the furnace.”