my advice would be gauge the tiles 1st , sweep and hover floor then seal with floor primer many choices, the check levels of floor , centre the biggest room or wall 1st , make a marking rod ( normal 6-8 tiles) check all runs off into different rooms spend time in marking out , find heighest point on floor and start to lay from that mark with thin tile but make sure you back spread the thin tiles as they be the 1st to fail, use a level checking tiles and floor as you go i mallet every tile old school, i normal make sure all edges are in full contact with adhesive increasing thickness as required , mark sure you work clean wiping tiles and joints as you go . check every 6-7 tiles that you are getting full contact. i normal wash slate 4-6 times with clean water to remove any dust of addy on surface , once you are happy i normal seal tiles before grouting and normally leave over night, i use rapid set grouts then there is no issues with staining , but slow setting grout maybe be better.
allow to dry then use a netrualiser to clean residue from tile surface allow to dry over night then put final top coat on slate ,
You must take you time , make sure you have wet cutter and please use gloves and eye protection when cutting ,
good luck and i hope this helps