It looks like the previous post has given an excellent link to the 10 steps to setup a new biz.
But i notice you question is in the insurance section so i assume you also wanted some pointers here also.
My husband is a Bathroom and Kitchen fitter. I do all of his administration and insurance. Try and get someone to help on the admin side as this free's your time up to fitting kitchens and making money. In addition, you need to get public liability insurance and employers liability insurance (if you have staff). I have had quotes from numerous companies over the years which can vary significantly. We orginally started off with the banks recommended insurance. At renewal i shopped around and nearly everyone cut the price in half. Never go with the banks its the same as home insurance - they charge a fortune. I found a company online about 2 years ago and they seem to be the best for this type of occupation, I have added a few extra options like 'tools cover', 'hired in plant', 'personal accident' in addition to the �5,000,000 Public liability cover and they're still cheaper than everyone else. More importantly the service is really good - which is important.
If your good at your job your gets lots of recommendations which is your future work setup.
Hope this is of use and good luck.
Link to below:
Public liability Insurance