On occasion, people who share this site are asked for advice about either finding or organising a group. Responding to such requests is always difficult because working with any group is a very personal thing and every case is different. It's not really possible to give individual recommendations without knowing the person(s) involved very well. That said, there are a number of points that come up over and over again.
They are normally discussed in the context of the "coven", the now common name for a group of people who follow the ways of witchcraft, generally referred to as "wicca". Most of these points can also be made about working with any pagan, magickal or occult group, from ceremonial magicians through druids to Carpocratian gnostics. They are also mainly common sense. Start off by thinking about selecting a group as carefully as you would a tradesman to work unsupervised in your house: most of the rest follows naturally. This analogy makes it simple to discuss the first point:
If you are starting out then you don't have enough experience to consider organising a group of your own. This is simple enough: if you wanted to set up in business as a plumber, first, you would learn to be a plumber. You could approach this in many ways. You could read a lot of books and practice on your own until you have the confidence to work on someone else's plumbing. You could go to evening classes and maybe eventually gain a qualification. Or maybe you would prefer to serve an apprenticeship with someone who is already qualified. But, regardless, there would be no point in advertising for business as a plumber if you didn't have a firm grounding in the basics of the trade.
Even when you do have the craft of plumbing completely at your fingertips, that's no guarantee of survival in the trade: to run a successful plumbing business you need other skills such as accountancy, which probably mean more training, and inter-personal skills which are normally best learned by watching someone else run a group. If you develop the habit of being totally honest with yourself (one which is vital in this field anyway) you will know when you are ready to organise a group. And, if you are honest, you'll also know that there are certain skills you still need to pick up as you go along. But by then, you'll know and trust enough people that you won't need advice from us about how to learn them. Forming a group before you're ready may seem tempting, but it risks damage to your personality, your relationships and your reputation that may prove impossible ever to undo.
Unfortunately, finding a group is difficult. This is partly because many groups are (with good reason) secretive. It is also partly because people, for whatever reason, have a habit of forming groups that they have no real ability to run and it is difficult for outsiders to tell the difference. So, first learn all you can about your chosen field. Read a lot - try to find opposing viewpoints and make assessments of which approach seems right to you. There are a number of "how to's" out there on the web, to which you have access if you are reading this. Once again, try to find several: only by doing so will you be able to make any assessment of whether the underlying principles are sound.
You can also find pagan meetings in most parts of the country (in the UK, at least: they're more difficult to find in many areas of the US, though not impossible). They are not widely advertised although occasionally lectures, particularly at universities, do make it into the newspapers. Try a local occult shop or bookshop if there is one near you, or, once again, look on the web. You'll find that certain names appear over and over again and with careful research you should be able to form some kind of view about the opinions the rest of the pagan community hold about those people. This may take a while and you may have to travel quite some distance to attend meetings: if you're not prepared to put that level of effort into the topic at this point, you're unlikely to have the dedication to follow your chosen path through.
If it simply isn't possible to travel, remember that virtually all of this can be done alone, or as a working couple, or in concert with a few friends linked by the internet. Joining a group is far less important than gaining the experience.
Finally, you think you have enough background to tell good from bad and you think you may have identified one or more groups with which you may want to work. The normal rule to start with is that if a group you don't know well asks whether you would like to join, you should be quite suspicious. Newly forming groups do sometimes advertise but otherwise it's normally wisest to do the leg-work yourself and gently approach a person or group have already got to know, perhaps at several pagan meetings, or at lectures or classes.
Be polite and friendly: mention that you would like to find a group. It's usually okay to ask if a group is looking for new members. It is almost never okay to ask initially for someone's real name, street address or telephone number and it is vitally important to remember the reverse - anyone who has your address or telephone number could make your interest known to anyone with potentially disastrous consequences. If the group holds public meetings you may be invited. If not, the normal practice is initially to meet in a public place - if an initial meeting with you is held at a member's house, consider very carefully how comfortable you will be with that level of openness once you become a member. Don't worry if you get turned down (if this is done rudely you probably wouldn't want to join anyway), everyone has to feel comfortable. If the group appears unnaturally eager to have you, consider what that says about its membership.
Once you have arranged a meeting with the group, assess the situation carefully. There should be time to do this: the traditional waiting period for a coven is a year and a day, but whatever the group, there should be no unreasonable pressure to join. The overall aim is to ensure that you feel comfortable with them and they with you. There are many points to watch but here's a personal selection of a few important ones.
Caution these people will eventually have the power to discredit you. Sure, they should be friendly, but are they taking the same care over their relationship with you that you would wish?
Willingness to Explain some rituals and techniques will normally be reserved for initiates. The basics, however, should be out in the open. Members of the group should be able to explain basic beliefs and concepts in a way that you understand.
Money it costs money to hire a hall, or to provide the necessaries in a private house. It's normal to pay for evening classes. These are legitimate expenses and normally the group will ask you to share. But, are the classes costing much more than equivalents in another subject? Is there a standing charge of more than a few drinks with friends would cost? If so, why?
Personal Attitudes does the group seem to be well organised? Does it share the responsibilities? Does it socialise outside meetings? Are people essentially enjoying it? These people will be part of your life - how sure are you that you want that?
Beliefs outside of the normal ethics, morals and belief structure, there may be aspects of the system ranging through ritual nudity and far beyond. Are you sure you're comfortable with the group's approach? Have you asked about anything and everything with which you may have a problem? Most importantly, were the answers satisfactory and if not, why not?
I believe it's traditional for the sergeant in an American cop movie to say "Let's be careful out there..."