1.) Research
Has anyone else in your area already seen these cats and taken action? Research online, then ask around. If you feel awkward just knocking on doors, put up posters. If you find information on your colony or loner online, somebody may have already taken steps like regular feeding, or even begun TNR. Also research people who do TNR in your area, and make sure the loner or colony hasn't already been treated or is about to be treated by that individual. Contact anyone involved to see if you can join any help efforts. If you don't find any information, and there are no responses, it's safe to continue. Keep up posters about your efforts, and possibly start a website dedicated to your cat colony.
2.) Observe
Take time to observe the loner or colony. At what time are the cat/s most active? At any time, where is / are the cat/s most likely to be found? When do they vocalize, or scavenge for food? Where exactly do they live, and is it private or public property? Make sure you are certain on the number of cat/s. Take notes on each cat's physical characteristics. Keep track if new cats show up or others vanish. Make sure that the loner or colony is indeed one or more stray/s or feral/s, and not an outdoors cat or already cared for by others. After several days, you should have your answer- and the cats should begin to notice you. Strays and ferals are normally crepuscular, but may also emerge in the afternoon to doze in the sun, or late at night when it is safely dark and quiet.
3.) Feeding
Set out dry food and clean water in bowls or plates nearby the cat/s's home/s at a time the cat/s are most active. Put the food down nearby cover, but within your sight when you retreat, because food in the open may make the cat/s nervous. Make sure not to use flimsy paper or cardstock. If you use pieces of plastic, make sure there are no sharp edges that could hurt the cat. Otherwise, plastic and metal work well. Set out food and water at the same time every day. You should make sure the cat/s are accepting the food and water, so you know you aren't wasting your resources. After setting out the food, don't hang around- the cat/s may be wary. Retreat to a distance safely within hearing or seeing distance- I suggest 50 feet.
4.) The Days After
Keep daily records of the cat/s. Begin to retreat to closer distances. Never frighten the cat/s- when you see signs of wariness, immediately stop any approaches made. One or more cat/s may be friendly and approach you. Let the cat do so on its own terms. Reward it with food. Don't try to pet or pick up the cat unless it truly appears to want you to- make sure you are not misreading its body language. If you are certain it is not feral, and is in fact docile, try to find its home. This may be done by posting FOUND posters, calling local shelters, researching online, looking through newspaper ads, etc. If you are incapable of keeping the cat, it is best to leave it where it is. If it's survived this long in the wild, it doesn't need you to do anything else. Sometimes, people with the intention of "rescuing" a cat from the wild, will bring it home only to unintentionally neglect it. Eventually, you will become an entrusted and acknowledged part of the cats' daily lives- but you will also be depended upon to show up with your customary food and water. They are now as much a responsibility of yours as a self-owned cat. If, for any reason, you cannot show up at the expected time with the expected resources, make sure to get a friend to stand in for you. Make sure the food is given at the exact same time and location. Your friend won't have to hang around because by now, the resources are customary, but they can if they want to- just make sure they retreat to a safe distance and don't try to suddenly integrate themself among the cats. After all, they are a stranger. Continue care for the cats, or find someone willing to take it on if you cannot.
5.) TNR
With the proper resources, TNR, or trap-neuter-return, would be your next viable step. It's self-explanatory- trap the cat/s, bring it/them to a veterinarian for neutering (and/or spaying), then return, exactly where you trapped the cat/s. For more, visit the TNR tab.
6.) Build Shelters
Here is a guide to building an inexpensive shelter from the Alley Cat Allies website (note: SSF is not affiliated with Alley Cat Allies in any way). Plastic bins work well, but always make sure there are no sharp plastic pieces. Shelters should be lined with Styrofoam or STRAW (NOT HAY). Plastic bins should be placed almost against a wall in order for a cat to crawl in and escape windchill and rain. T-shaped or L-shaped shelters work great if self-built, with an entrance tunnel and the room for the cat.