The widely-held belief that a conductor’s job is to follow a soloist is rarely accurate. Rather, it is our job as conductors to learn what the soloist wants at different places in the music, then make it happen by leading. “Following” a soloist rarely gives them the accompaniment they need, because if we are following, we are by definition behind them rather than with them. (One notable exception is that when departing from a fermata, we usually follow the soloist’s lead.)

But that brings us to the hard part: learning to tell the difference between intentional, interpretive tempo changes and unintentional changes of the kind often caused by technical difficulty in the solo, a weak sense of rhythm/tempo, or worst of all, inconsistency from one rehearsal/performance to the next on the part of the soloist. And that isn't so much about learning to accompany as it is about using our musical experience to recognize which sections should be cruising along at a constant tempo and which ones lend themselves
musically to ritardandi, rubati, etc. In other words, many of the considerations that come into play accompanying are the same as those we bring to bear interpreting anything else we conduct.

I’ve always felt that accompanying soloists is the hardest kind of conducting. I thought I was pretty good at it until the Coast Guard Band added a vocalist to our complement. She sang a lot of opera excerpts, which have more fluctuating tempi than constant ones, and I grew more as a conductor in the first couple of years she was with us than I had in many years before that.

But you don't have to be accompanying opera to develop your own accompaniment skills; and a good first step is understanding that following is not true accompanying.