There are few things that contribute to sharpness, and also some issues that apply to all digital cameras that you should be aware of.
Things that can rob sharpness:
- Camera movement. It sounds like you have this handled well, using a tripod and remote. The D50 however does not have a mirror lock-up mode or mirror delay so I'm not sure what you're doing regarding the mirror. Generally mirror vibration is only a problem in a specific shutter speed range (1/15-1/60 or so) so if in testing you find this is a problem, you can avoid these speeds by changing ISO and/or aperture. You can help reduce vibrations further by "loading" your tripod, hanging weight from the center column, or even leaning on it during exposure. The quality of your tripod and head are critical as well. If these aren't high quality, then all bets are off.
- Focus. If you are missing focus this will certainly affect sharpness. You can experiment with this with a static subject by first autofocusing, shooting, then switch to manual and take subsequent pictures with micro movements of the focus ring. Hopefully the AF shot is the sharpest, otherwise you have a problem that could be camera, could be lens, could be electrical contacts between the two.
- Subject movement. Here you just needs shutter speed fast enough to freeze your subject, if it's moving. For humans this is probably in the 1/150-1/400 minimum, depending on how fast it's moving. For birds, closer to 1/800 or faster.
- Depth of field. If you don't have adequate DOF then some areas of your photo will be sharp and others will appear out of focus.
It would be helpful to see some actual photos so we can help diagnose, but that's the general scoop as I see it.
On the subject of digital capture, and this is true of all digital cameras (some more so than others), the sensor has a filter on the front that slightly blurs the image. This is to prevent "moiré" patterns from emerging when the frequency patterns in the subject are close to the spacing of pixels in the sensor. The classic problem is taking portraits and the fabric of the person's suit takes on all these bizarre patterns. It can occur in landscapes as well in the textures of rocks and grass. Google moiré to get a better idea of this, but for practical purposes what you need to know is that digital cameras that are known for being very sharp "out of camera" are also prone to moiré problems. The Anti-Aliasing filter helps prevent this, but at the expense of initial image sharpness.
The takeaway from all this is that with digital capture, softness in unprocessed images is natural and there for a very good reason, and sharpening your images in post processing is therefore a necessary part of the digital workflow. You can set up your camera to sharpen for you, however as you get serious you'll probably find you need more advanced techniques and you'll do the work in post processing.