Here are my opening lines. The a) lines are for a story I started for the previous prompt. I'll put a description at the end so you can see if your impressions match where I was going. The b) lines are ones that may lead to a story some day.

Classifying an opening was harder than I expected. Most lines I wrote could have fit in multiple categories.

1. Show us something interesting about a major character (ideally the lead protagonist).

a) Mark woke but couldn't see or hear; as usual the humans were slow connecting his sensors.

b) Jacob opened the paper and started reading. Behind him a portal opened and the spirits started to flow through.

2. Set something unusual and interesting in motion.

a) "Mark, I've started the memory downloads from your backup but the latest events were lost in the battle."

b) The stars twinkled in the deep black of outer space. Stars don't twinkle in space but incoming missiles do.

3. Establish the setting with a striking detail, ideally one that sets the mood.

a) Mark turned on his sensors but they didn't show the ship's bridge as he expected but a lab with a human watching some screens.

b) The young dragons played tag in the sky while below, too large to fly, their parents watched and with their fiery breaths roasted the unicorns they had caught for lunch.

4. Introduce an unusual relationship for the main character (with other characters, himself, his surroundings, and/or the readers).

a) The doctor looked at Mark's readouts and said, "You're running a bit of a fever. Your CPU and memory systems are a few degrees warm so I'll have to reduce your frequency until we figure it out."

b) "I do," I said because I had always dreamed of marring a girl with deep blue eyes and three out of five of hers were blue.

5. Introduce problems and/or conflicts.

a) "I don't care if he saved thousands of troops. The farm worlds are full of boys and girls waiting to enlist. It lost a battle cruiser. Change its priorities so next time it saves the ship instead of the troops," the Admiral said.

b) The door flew open and three women entered with guns drawn. Had I forgotten their birthdays again?

6. Subvert expectations and/or set up eye-catching contrasts, like exploding grandmothers.

a) "I know a medal is in order but am I supposed to glue it or weld it to its housing?"

b) We need to grease the elephant before loading it into the landing craft.

7. Bad opening

I knew I was in a dream because the weather was perfect with only noctilucent  clouds, which are cirriform clouds that occur in the mesosphere above 264,000 feet, dotting the blue sky and not towering cumulonimbus to dampen my spirits.

The a) lines are for a story about an AI captain of an interstellar battleship which had barely managed to survive a battle and is recovering in a military base in preparation for its next mission.