When shooting a camera, as was already said, your heartbeat will have an effect which you can see if you look for it. If you use the camera more like a rifle, you can get those long exposures. Use a rest, any rest. It can be a rock, beanbag, tree trunk, anything. Just leaning against a tree will help. Borrowing positions from rifle shooters such as sitting and bracing against your knee help too. You want as many points of support as you can get. Slowly breathe out as you press the shutter. Don't hold your breath that makes it worse.
For tilting a baseboard or easel, use a piece of graph paper. It makes it much easier to get the lines true. Without it, I always tend to overcorrect.
When using a tripod, if it does not feel steady enough, just add weight. Hang a barbell plate, bag of rocks or spare camera from the center post and let it dangle.