get used to riding close to people, that’s going to be the main thing for most people coming from tri to something like a crit.
In my experience when we put on beginner crit series (or were…) triathletes that came to the Beginner/5 race almost always ended up just TT’ing the race, either off the front or off the back. I can’t think of any of them that raced in the pack. Even if you’re the strongest person there (often the case for a pretty good triathlete) you won’t learn anything about bike racing sitting off the front/back, and if you take a liking to bike racing, you will not get very far at all just being strong.
not ending up on the ground isn’t something you can guarantee in crash 5 road races or crits. If you aren’t ok with the possibility of eating sh*t… don’t line up, because most people do end up on the ground at some point.
This part can’t be overemphasized enough.
As to the OP, there are three main components to doing well in a road race: the tactical part (as in, how good are you at reading a race and conserving), the technical part (as in, could you maneuver without endangering others), and the physiological part (have you trained to handle the demands of road racing).
Tactics, one learns from watching how others do it and via practicing. Reading race reports and soliciting advice from those more experienced (see the threads below). This also include how to do things efficiently, such as moving up within a pack (as opposed to side blasting). Things that are quite easy to do (technically and physiologically) but require planning and a bit of forethought.
Techniques has to be learned from doing. Group rides present one aspect of it (how to ride in a group without causing a crash), but it doesn’t do other things well (e.g. cornering).
Physiological part is the easiest to implement in training but hardest to do. Road racing is all about recovery from effort, and it’s drastically different from what pseudo-steady state efforts such as triathlons and ITTs. One has to be prepared to do some really difficult stuff, recover while still going at a decent clip, and then hit the gas again. In that vein, some of the Zwift racing isn’t too bad a simulation of this, especially the short circuit races. If you can at least manage to do decently in a C-level Zwift circuit race (as in, staying with the front group), you at least could be decently prepared for the demands of a crit. If you find yourself getting dropped after five minutes, you need to work on your training.
Also, a few previous threads for your perusal (basically answering concerns similar to yours)
https://forum.slowtwitch.com/...ad%20racing#p7256257
https://forum.slowtwitch.com/...string=crit#p4980482
https://forum.slowtwitch.com/...64/?page=-1#p6562017