Lightweight Object or Pictures
Extremely lightweight objects can be supported with a piece of tape or a glue on picture hanger. The walls must be smooth, clean and dry with the paint adhering well. The glue is affected by humidity and aging and may let loose so do not hang anything that will break with this kind of fastener. Objects with a wide variety of weight can be supported by a metal hook on a long tapered nail driven at an angle into the plaster. These come in packages of different sizes depending on the weight to be supported.
Medium Weight Objects
Some kind of insert, plastic, fiber, wood. or lead can be used with a sheet metal screw. Drill a hole just large enough to be able to tap the insert into the hole. Tap the insert into the hole until it is flush with the surface. Turn a sheet metal into the insert. Usually these inserts come packaged with the right size screw for the particular insert. It will also tell you what size hole to drill.
Heavier objects can be supported with a molly style hollow wall fastener, a spiral threaded fastener, or a toggle bolt. Any may need a flat hook attached for picture wire. Drill a hole through the wall to fit the size of hollow wall (molly) fastener - be sure not to get the hole too big or you may have difficulty turning the bolt without having the connector turn.
If the only drill is too small, use a small screwdriver, knife, or round file to ream out the hole until the fastener will slide in snugly. Push it in and turn the bolt clockwise many many revolutions until it feels tight and flush to the wall. Now the fastener has expanded and should stay tight. Remove the bolt and attach the object screwing the bolt in tight. Do not over tighten or you may pull the fastener loose.
Remember plaster is soft. A Spiral threaded fastener cuts it's own hole, and uses a separate screw into it's center. Do not use these overhead. A toggle bolt can be used similar to a molly bolt but with less care taken when installing. Unfortuneately it requires a bigger hole.
Select a bolt long enough to include the object plus the wall plus the length of the toggles when folded up. Drill a hole through the wall. If you do not have a drill: Drive a nail through the wall.
Wiggle it until it comes loose and you can pull it out. Put a small screwdriver, knife, or piece of metal into the hole and carefully enlarge until the toggle will slide through.
Assemble the object on the bolt and push the toggle into the hole until you can feel it spring open. (Now you cannot remove the bolt without losing the toggle in the wall).
Tighten by turning clockwise. A toggle bolt should be used where the object will be drawn up tight to the wall because the hole must be large enough to receive the toggle. The object should be large enough to cover the large hole that is necessary.