My FC in this game is just a personal one for my husband and our two close friends, but I run a raiding guild in WildStar and your concerns are fairly universal.

I've found that having a Discord server and using it to chat when we're not in-game has really helped bring our members closer together. It also allows us to maintain connection to individuals who PUGed with us in the past and who enjoyed running with us but may be part of other guilds - which provides a good source of other people willing to do various activities.

We also make a point to do things together outside of our scheduled raid nights. These things won't just happen organically - it's kind of the responsibility of every member to log in and make requests of other members, be it for running Prime content, hunting world bosses, leveling or attuning alts, helping with a housing issue, etc. FFXIV equivalents might be farming trials for weapons or mount tokens, S and A rank hunting, or helping someone with tomestone grinds. I think doing stuff together outside of raid night is critical to maintaining camaraderie in the guild and for member retention.

If you've just achieved a major guild goal, then take a little time to celebrate before discussing as a group what goal you would like to next set. Not only will this bring in more ideas to the pot, but it will give the members a stake in the guild and playing together.

[edit] I have found that in FFXIV, a lot of the "raiding" scene revolves around linkshell-based statics that often do not have the same level of group loyalty as a raiding guild in other MMOs. Honestly this is one of the reasons why I don't really raid in this game, BUT I think the strategies mentioned above can apply to really any situation.