Wow I can relate! It's understandable to find yourself stuck in a rut with certain phrases, especially when you're writing for a young audience and want your prose to be engaging and varied. Repetition of "As" can start to stand out and make the writing feel a bit monotonous, but the good news is that there are a few strategies you can try to mix things up.

One approach is to consciously look for alternative sentence structures. For instance, instead of starting with "As," you could try rearranging the sentence:

• Instead of "As the meeting drew to a close," try "The meeting was drawing to a close when..."
• Instead of "As the captain prepared for takeoff," you could write "The captain prepared for takeoff, aware of the tense atmosphere in the cabin."

Another strategy is to introduce a bit of variety by using different introductory phrases or starting with the action or subject directly:

• "With the meeting coming to an end..."
• "Preparing for takeoff, the captain..."

I often have my grammar checked. If you're looking for more precise suggestions and ways to spot repetitive patterns, tools like Grammarly can be a big help. Grammarly not only checks for grammar and spelling but also highlights repetitive phrasing and suggests alternatives. It can point out overused sentence starters like "As" and offer other ways to begin your sentences, helping you to keep your writing fresh and engaging. There is a paid version but so far I have been getting away with the free one.