Boots and ski's

I tend to agree with this advice. I bought boots before I bought skis, but I ended up buying the skis very soon after the boots.
Take the advice re fitting and trying on, and make sure the shop will offer you a refund or do some adjustments if you have any problems with them on the slopes.
Rental skis should be ok, and you can always take them back. Go for the highest grade you can afford, you'll get newer and better models, and try different types of ski during the week - carver, freeride, all mountain, etc.
If you are looking to buy skis, Sport Conrad is as good a place as anywhere if you know what you want, cheap deals with bindings too.
Get used to your own boots before you delve into buying skis, and try out different sorts as mentioned.

Boots first and foremost; take your time, try on as many pairs as you like, make a fuss, keep trying them on, don't be afraid to make a nuisance of yourself, ask questions, sit down, walk around, dance about a bit, simulate ski movement, ask about footbeds and have them fitted. Any decent boot fitter worth his salt will expect you to do this. Take hours if you can.

When I worked in a ski shop, I sold this customer a pair of boots that he decided on within three minutes were for him (I think he liked the colour). I pleaded with him to try others, to at least put a pair of ski socks on while trying them (!), to take them out on the artificial slope and have a go in them, etc etc. But no, he was adamant. I hope he enjoyed using them - but somehow I doubt it. It was a grim experience for me, but he was convinced he was right and would take no advice.

As for skis (no apostrophe needed!), maybe try before you buy is the best advice. Rent a pair or two or three or four, see how you go and then decide to make a purchase, or not, as the case maybe.