Try different magnifications. Sometimes using more power when looking at a galaxy will make it easier to see. When looking at emission enbulae try using a narrow band or line filter nebula filter. Make sure your telescopes optics are clean and well collimated. Make sure your eyepieces are clean.
Some nights are better than others.
Seeing and transparency can change a lot even on the same night. Try to find the darkest site possible. Try a bigger scope. If you know were to look when trying to see structure in a DSO it can be a big help. If you don't have access to a larger telescope find a photo of the object.