Training the trees to have good angles on the limbs and training yourself on when what to spray. The local Extension agent can really help here.

Here is a link that might be useful: UT Extension home page

For the first 2-3 years you need to make sure when the new branches sprout out that the angles are kept at 45 degrees or less from horizontal, and if not, then prune them off or weigh or tie them down so that they are. Clothes pins can be handy for this -- clip a clothespin to the central leader with the side of the spring pressing down on the new branch while it is still young and green to keep the angle low.

Another thing is when the branches become too crowded, you may need to do a little thinning. But for the most part, young trees just need time to grow out. It will be a couple years before they produce any fruit unless they are already several years old at planting time.

One other thing I like to do is if the trees grow up way too tall -- I mean like 9 feet high, so that you won't be able to reach the fruit up there -- then you may wish to lop the top off each year so that the fruiting wood stays low enough for you to be able to pick it later in the tree's life.

I guess I've assumed that you want a pyramid-shaped central leader tree. You could also do an open-center vase-shaped tree. There are different techniques with many books and resources about each. Figure out what you think will work best for your orchard and stick with it.

Have fun with it.

Buy "The Pruning Book" by Lee Reich. Normally I just get the books I want from the library, but after checking out the same book several times, I figure it's worth it to own it. Another fruit tree-specific book will do, of course, but it's nice to have the advice for all types of pruning.
Don't worry too much about the trees, if you keep them watered once a week and check for diseases, they'll be just fine!

You need to know your pests, for instance, are there a lot of squirrels in your area? If so, you may want to eventually leave the first 4' of trunk branchless and develop your tree from there so you can attach a baffle and squirrels can't jump to the branches from the ground. Coons and possums can be discouraged with only 3' of trunk that has something hard and slick attached to it all the way around.

You need to know your rootstocks as how you train your apples will depend on this as well.

Plums you will probably elect to shape as open center to help reduce brown rot pressure, but apples on semi standard (M7 on up) give you a choice- central leader of open center. I actually think for beginners the advantage may be to go with an open center- the point of a central leader is to maximize production which is not much of an issue in a home orchard as getting 10% more fruit from same space just isn't very important in the face of the wide range of factors that will determine if you get fruit at all.

It would have been easier if you'd come here before the purchase but it's all a learning process and this is a wonderful hobby if you have a bit of patience.