On the recommendation of a moderator, I provide here a partial answer to your situation, which does not answer your question in general.

You specifically want to improve the emotion in your descriptions and NPCs, so take introductory classes in creative writing and/or improv acting. Those people don't know anything about GMing, but "evoking emotion in the playing of NPCs" is acting, so if that's what you want to improve then approach it as improving your acting.

There may even be free or nearly-free amateur improv acting in your area.

Of course, this would not apply to an experienced GM who has the acting nailed down but needs to improve some other aspect of their play. They would have to identify their own weak areas.

You specifically want to improve the emotion in your descriptions and NPCs, so take introductory classes in creative writing and/or improv acting. Those people don't know anything about GMing, but "evoking emotion in the playing of NPCs" is acting, so if that's what you want to improve then approach it as improving your acting.

There may even be free or nearly-free amateur improv acting in your area. If you can take your players (kids) with you then all the better.

Of course, this would not apply to an experienced GM who has the acting nailed down but needs to improve some other aspect of their play. They would have to identify their own weak areas.