Image Sharpness/Detail

I'll echo the good advice above about steadying your camera when using a telephoto lens. The longer the focal length, the more pronounced even the slightest camera movement will be. An ounce of prevention is worth an hour's worth of post-processing work. A tripod, wall, fence post, tripod head on a suction base that can be fastened to a vehicle, a bean bag — anything you can bring or employ to steady the camera will be a big help when shooting telephoto. In less than great light that goes double.

Of course, you want to favor smaller apertures for greater depth of field, but keep short of where diffraction sets in. And, fine-tuning focus can sometimes help ensure the best possible sharpness in your center of interest.

Lastly, keep some healthy perspective about what you intend to do with your images. Pro's who do work for advertising agency and publication art or photo directors must deliver super sharp images unless a particular subject calls for something else. Some of the pro's images are used for huge enlargements.  For your purposes, if most images will be viewed on screen and some printed snapshot size, with a very few enlarged for framing and hanging on a wall, your need for super-sharp images is less. As others have mentioned, what you see when you enlarge an on-screen image to full size (pixel peeping) is extreme. Photos enlarged to hang in your home or be part of a photo album or book can look and be excellent even if  they're not perfectly sharp and quite so splendidly detailed when pixel peeping.