Fitting a slide rail to your shower:
Try to buy a mid range priced shower rail as usually they are made of metal and outlast the cheaper plastic ones. Also there are some really excellent sprays on the market now. They do not come cheap but for all the times you are using the shower it is money over years not months.
Remove old shower head rose spray and with either an off the plumbing shop shelf barrel nipple or some nippling brass threaded tubing custom cut as is described under the heading Replacing or placing a tap into a wingback in the wall: Connect the wall to shower hose fitting using PTFE plumbers tape.
Then attach the tapered end of the shower hose to the new spray head and attach the other end to the out of the wall fitting. Just allow the hose to dangle into the shower tray or the bath while you carry on and fix the shower rail proper as follows. Take out screw packet and remove raw plugs, as you will be needing them if you cannot strike timber to fix into. Go for a drill bit about half the diameter of the raw plugs and a slightly bigger drill if needed after trying the first drill out.
Have a dry run at piecing together the slide rail anchor sections with the rail itself. Sometimes it is easier to pop out the end caps that hides the screws, by punching them out, with a long thin screwdriver. Place your first anchor on the wall near the height of the wall cladding or at about 6-feet (1.8 M) off the from where your feet are. Note: The rail itself does not mount center exactly as the spray head is offset by about 2-inches (50 mm). Mark your top most anchor and drill the hole being careful not to allow the drill bit to rush through into the wall cavity as there are plumbing pipes inside this wall.
After finishing the first hole have a go at fitting the raw plug and if the hole is too small go to the bigger drill size and then fit the raw plug. Then screw the anchor in place and holding the rail up into the anchor mark the hole to be drilled for the bottom anchor. Drill this hole now and place the raw plug and screw the anchor to the wall. Pop in the cover plates. Place spray in holder and adjust it to match your showering requirements.
Note: Do not forget to fit the soap tray before placing the last anchor.