Emasculate or cut into a flower before it opens to remove anthers and pollinate before any pollen ripens. This is first and foremost if one wants to be safe and is especially important if one has a species that can self pollinate. Not that pollinating early like this is not helpful otherwise as one never knows what insects might help one if one does not visit the flower early like this. Note, I cut the flower open with a simple razor blade being careful not to remove the style and stigma completely. This little girl has been pollinated by myself and no insect has had a chance to do its dirty work.