You will be able to find a full list of areas local to you, with directions of how to get there, safety advice for each particular site, and a message board to see who else may be going at certain times. Once you have found an area you would like to visit and arrived there, what do you need to do? You will often spot other people walking around on their own, maybe looking at their phones, or just slowly looking about. It is unlikely that someone will just walk up to you and announce what they are there for, so it is important to keep a look out for signals, such as eye contact, a nod of the head, or something along those lines. If this happens, it generally means that they are interested and you can approach them.
Making sure you are safe at all times is of the utmost importance. Due to the types of areas you are visiting, it is very unlikely that there will be CCTV in operation, or even lighting. It is advisable to keep all your personal items, such as mobile phones, wallets, and keys, well hidden on your person at all times, or leave them at home if you can.