DSLRs, as 35mm cameras, have shallower DoF (Depth of field) than digicams. Good for portraits, bad for landscapes. Also, manual focus errors are less forgiving, mostly with tele lenses or wideopen luminous lenses as the 50/1.8. When using manual focus, check if the illuminated point is the intended, not another one, or focus will be done elsewhere. You can't choose a focusing point during MF, so the focus assist will beep when ANY point reach focus, not only center one (or the previously selected one).
Also, to avoid blur, there is the "shutter speed > focal lenght" rule of thumb. This was valid for 35mm focal lenght, so in digital the rule must be read as "shutter speed > 35mm equivalent focal lenght". That's means you must multiply the lens focal lenght used by the crop factor (1.6x in the dRebel). So for a 50mm lens, you must use at least a 1/100 shutter speed. Of course this is only valid for camera shake induced motion blur. If the subject isn't static, and you are using a 35mm equivalent 28mm lens, a 1/30 shutter speed probably will be too slow. Try not to shoot anything below 1/125 if the subject is a moving one. Of course some lenses break this rule, as IS (Image Stabilization) lenses, because the IS allows you to use a slower shutter speeds to gain 1.5-2 stops. So a 300mm IS lens can be used at 1/125 instead of at 1/500.