TURF: apply weedkiller containing glyphosate (eg Roundup) to area to kill off pereniel weeds and weed grasses. Take up old paving slabs and any bedding they may have been on. Hire a good rotavator. Rotavate to 150mm, roughly level removing debris, r/vate again to fine tilth, consolidate by shuffling back and forth (looks a bit silly but it works) Rake over and grade again, removing any debris over 25mm dia. Apply a base fertilizer (eg growmore) and lightly rake in. Water surface (dont walk on it again!)working off boards, start with nice straight row, then working from boards on turf, away you go, not forgeting to halve the joints. Make up a wooden beater and 'pun' the turf, water and dont let it dry out.
PAVING
A concrete base is always better. For a patio we use a 75-100mm concrete base and bed the slabs on sand/cement bedding mix.(I dont want any comeback!) Some slabs will butt joint and some need to be pointed with 3/1 mix soft sand/cement.
DECK
If your deck is raised, then 150 x 50 bearers are required at 500 centres. A G/L deck will need 100 x 50 bearers at 500mm centres mounted across rows of brickwork at 1250 centres with dpc membrane protecting the timber...............or just make up a big frame of 150 x 50 timber and slap it down on the bare ground per that well known TV make-over prog. Oh yes and use screws, coach screws, bolts and more screws - forget the nail gun!!