First you have to decide where in the country you would like to be. You can choose say 2 or 3.
Secondly do you want touring caravans, static or a mixture. What facilities do you want to provide other than basic, ie a shop, childrens play area etc. How many months a year you will open.
Thirdly go to see the council planning officers in the areas you would like to make your park. You will need to know what there views are on a new development , they may consider there are enough, there may be restrictions in some areas or they may welcome you with open arms.
Then start looking for land in the areas most suitable, if you find anywhere suitable before you buy go back to the council and ask what are the chances of planning permission, if agreeable make your offer when accepted see the owners of neighbouring land or property and explain what you intend to do, this may not be favourable in their view but it is better coming from you than in a letter in the post. Before you actually sign for the land go back to the council and get outline planning consent for the sort of park you want, it is at this point neighbours etc can object, once you have planning consent then buy the land etc. and make your park.
Don't just see somewhere buy it then find out you can not get planning permission. Good Luck.