Here's my 2 cents as someone who went through this process twice after coming back from 2.2 to a few weeks before 2.55 with success. I say twice because first post was before I ever stepped into fcob, thus had fewer interested parties or upon investigation with lodestone felt my skill level was higher than the groups replying. This latter issue may seem elitist and not apply to you. But I didn't want to be stuck with a group as the top reply to OP brings up that I felt I was better than (i.e. thinking my coworkers were bad). Ultimately though such a group may be your only option and if this is the case treat it as an entry level job. I also learned from mistakes joining a toxic group too quickly in an FC I didnt fit in with socially.
Figure out what you want within the constraints of not sacrificing your real life. Do you want to be hardcore? Do you want to see if you could be if you haven't before? How many days are you willing to raid as a maximum or minimum and what is your flexibility with hours on those days. Obviously you'll have varying degrees of options depending on both and what server/data center you're on.
Your initial approach should be to post in r/ffxivrecruitment, OF, and PF. Bump or update those as often as is allowed (i.e. weekly for the subreddit or the OF and daily for PF) and regularly search listings in those places as well. You need to be flexible with positions so offer at least two roles you're proficient in and save esoterics if you want to indicate your flexibility for what the role you play will be or which job in that role. Learn and practice rotations for those rolwa to maximize dps if you don't know one too well and save some or all eso to indicate that flexibility. Ask friends to look out for openings for you.
Any group you would want to join will trial you to a degree and may do a background check of sorts with asking around about you (depending on the group this may be just how drama/toxicity you bring to a group or they'll want parses, videos and maybe even essays (be wary of those last two unless it's Elysium or a similar high level guild lol).
YOU need to do the same. Trial them. Ask why the last person left, ask friends about the reputation of the group and its players and engage them socially to see how you will fit in, i.e. TS and what they do as a group besides raids (i.e. PvP, maps, etc.) Look at lodestone and try to see achievements to see their approximate skill level before something is on 'farm'. If they won't take you in ask if someone will stream or if they'll let you be in TS observing if they aren't taking you.
I didn't do any of this well enough with the first group so I didn't see the skill level disparity, high turnover rate of players, toxicity and lack of follow through on goals (i.e. saying we'd do savage scob then just farming ponies or fcob instead). I basically hung around out of loyalty for 2 months for giving me an opportunity, but eventually the problems and prospect of 3.0 raids with them outweighed that loyalty. I gave my two week notice but when the leader started personal attacks upon our talk, I just left.
Second group I followed the advice I'm giving. I joined with the mutual understanding that it was a temporary spot just for t7 savage with the possibility of a 3.0 spot while I weighed options. I clicked socially almost immediately and saw that the skill level /attitude and raid times of the group was what I wanted out of a group and asked if I could have a permanent spot after a week and a half with them.
Unfortunately because of the timing with few spots mid raid progression and active competition from a3s capable players whose groups fell apart you may need to take that entry level position and bide your time for 3.2. Commit fully to whoever you join but keep an eye out starting in 3.15 for a group using the methods I gave if you don't fit in with the one you joined or want to experience something different (i.e. midcore to hardcore or casual to mid, etc.)
Hope this helps and didn't come across too douchey and elitist as my goals may be different from yours.