If it hasn't leafed out much you should be OK. You don't mention how big or old the tree is but you've got to remember that the tree's biological imperative is to produce and spread a lot of seed, not a lot of fruit. Few fruit trees will produce good quality fruit if they aren't pruned to a quantity of branches that will allow the tree to grow fruit or good size and quality.
Here's some thoughts based on not knowing your tree. First get rid of the dead branches. Then take out any that head back into the tree. For any further pruning, picture yourself above the tree and looking down and try to leave a uniform density of branches radiating out from the center. Use a sharp saw or shears. The less the amount of tearing and ragged ends you leave the less chance there will be of rot or infection later.
If a branch is too heavy for you to hold up and support while trimming then undercut it a bit and cut it off outside the undercut. Do this a little further out that your desired final cut. Now, make the final cut without any worries of a split branch or ragged edge.
Think in terms of leaving three or four layers of branches (as viewed from the side) with room between the layers for air and sun to get to the inner parts of the tree and so that the branches aren't rubbing on each other either now or when they hold heavy fruit.
Don't go to crazy. Most apple trees will tolerate up to one third of their branches being cut out at once but that's likely far to drastic for a first attempt. You can always prune more next year.
I'm sure an internet search for something like "apple tree pruning" or "apple tree pruning basics" will give you a lot of info, too. If you are going to have even a few fruit trees you may want to buy or hit up a library for a copy of "The Backyard Orchardist" by Stella Otto. It's a good book that's pretty readable. It has helped me a lot here on our farm as we've developed a small orchard.
When the fruit sets you may want to pinch off some of the small fruits-maybe one third-to make the tree concentrate on growing fewer but higher quality apples. Try to leave an even distribution of fruit and if there are any particularly small branches make sure you don't leave so many fruits on them that it risks breaking the branches when the fruit gets larger (think "windy day" here). Discard the fruit you pull off and don't drop it in under the tree. You don't want to encourage any rotting of fruit or prunings around your trees so get the branch cuttings away from the tree, too. If you don't have curbside pickup then burning is preferred. A lot of rust, bug and blight issues start in rotting fruit and trimmings.
Any good local nursery that sells fruit trees can advise you on local tree health issues and pests. You can decide if you want to do any spraying after talking with them.
Good Luck
Lance
