What is the general rule of thumb or general rule for the treatment of a superficial foreign body in the eye?

If it is a chemical, flush it outwith water away from the other eye.

If it is a small grainy substance like sand, try flushing with water. If it doesn't work, call and wait for EMTs.

If it is a rock or other large object, DO NOT TOUCH IT. You may embed it further by trying to remove it. Unless you are a trained professional, don't try to get it out, you'll probably make it worse.