1. If you drew an object that you didn't intend to draw, use the eraser to remove it instead of undo.
2. If you did a push/pull operation no that you didn't want to, do a second push pull operation to get back to the original position instead of undo. Note you can type distances distwnces for operation or snap to other geometry.
3. If you deleted an object you didn't intend to then redraw it instead intend of deleting it. If you deleted a lot and don't want to re-draw it you can close the model without saving and reload the last saved version.

One additional note I will add. If you are just drawing loose SketchUp geometry that isn't part of the OpenStudio model yet, such as a floor diagram that you plan to later extrude, you can use undo.