1. Speak to a few flying schools, get a feel for them, the instructors etc. Choose one club and book a trial flight.
2. Save some money. To complete a PPL in the UK in the minimum number of hours will cost circa £10k. Note I say minimum, most people need more lessons than the minimum, at extra cost. A lot of people run out of money so best have it set aside, it is one less thing to worry about.
3. Look in to all the options of where and how you want to train. In the UK or abroad, intensive 4 / 5 week full time course or one or two lessons a week, the latter will probably take about 1 year to complete.
4. You will need to sit 7 theory exams, these are multiple choice. Start by reading up on the subjects. Again your flying school will recommend good books. I used Trevor Thom and 'The Confuser'. The more exams you can do before you get in an aircraft the better in my opinion. Certain exams must be completed before you can do certain flying tasks e.g. you must pass Air Law exam before you can fly solo and I had to pass Air Nav exam before I could so solo X-Country.
5. Choose a school and instructor. Check out aircraft and instructor availability. How well are the aircraft maintained? NEVER pay upfront for the whole course, people have lost a lot of money doing this. Though schools do offer discounts for blocks of flying, so you can pay for 10 hours and get a discount, this limits possible losses but is up to you to decide if it is for you or not.
6. You will need a class 2 medical, assuming you a reasonably fit and healthy this is nothing to worry about, but best to have it before you spend a fortune
7. Enjoy it! You will struggle to maintain airspeed at first and landing will be the impossible task that you think you will never be able to manage, but you will get there.