  After a site testing campaign spanning 5 sites over a period of 5 years, the
site selection for the Thirty Meter Telescope (TMT) culminated with the choice
of Mauna Kea 13N in Hawaii. During the campaign, a lot practical lessons were
learned by our team and these lessons can be shared with current and future
site testing campaign done for other observatories. These lessons apply to the
preselection of the site, the ground work and operations of the campaign as
well as the analysis of the data. We present of selection of such lessons in
this paper preceded by a short summary of the TMT site testing activities.
