In my experience (that is mostly on D&D, not SW), it is the players that determine which NPCs are memorable or not. Your role as a GM is mostly to notice which NPCs they like more, and find out why they like it.
In general terms, you should remember that the NPC roles are to complement the party abilities, not to overshadow them (that would be the mary sue NPC types) or be a burden on the team. When I really want the players to like an NPC, I did the following with them:
Give them an objective
Normal NPCs that don't have to interact with the party further than a few lines don't need much characterization. But a long-term NPC ally should have a strong reason to trust the party. They might be using the party to reach their objectives (the nature of such objectives being good or bad is irrelevant), they might recognize that the party is stronger than they are and the ones that might be able to pull it off, they might even just really be good friends with a party member.
The point is, they have a reason to act alongside the party in the first place. And even if those reasons are not out in the open to the group, they will be implied when you actually have those objectives in your GM notes, instead of just thinking they should be friendly because they should be friendly.
Give them a quirk
No one remember the man with the phone #6 that walked on the background. Everyone recognizes the woman in red that turns into an agent.
When you first describe the NPC, give them something memorable on first sight. Or give them a unique accent (funny or not is your choice). Or make them fall in love with machinery, or talk about the rights of summoned creatures, or end every phrase praising the sun.
Don't overdo it, however. Do it just enough that when you start praising the sun, everyone knows you are talking about that NPC.
Remember that they are not omniscient
It is very, very, VERY common to see your party struggling with something story-related, and you give in on the urge to make the NPC point out something that might be obvious to you. Things like "have you tried to ask whatshername?" or "don't you have an ID card to bypass that?" or "why no one checked the altar yet?"
While this seems like it will help move the story forward, this actually removes agency from the players. The only instance where this kind of advice is ok is when you are dealing with the specialty of such NPC, and eve then, don't give out more info than the party is asking for. A ship mechanic can give out advice that the engine is making a weird sound, but unless the party asks her to check out the engine to find out anything problematic, don't make she check the engine on her own.
Remember that your NPC is not a protagonist
By definition, a protagonist is the person (or persons) who the main story is about. In the end, what really matters is what your players seek and do, not the NPC. If they decide to help your NPC and completes his quest, don't come with a new quest just to make them relevant again. If the NPC still tag along the group, he will be grateful that the party solved his problem. And that is it. He don't have anything else relevant anymore.
(Unless, of course, your party decides that this NPC should be helped more. Then you start bringing more problems with them. Otherwise, no)
Don't force the party to like your character
Let's say you did everything right. You made a fun NPC, someone that will not steal the spotlight, and that will only give some vague advice because that is all they have. The party still think she is annoying.
Shrug off, get rid of the NPC as soon as possible, and start working on the next one. The fine tuning of what clicks for each group varies a lot. I had groups that like when NPCs point them to the danger and unleash. I had groups that love when the NPCs actually antagonizes them because it makes them use better arguments. As long as you are willing to experiment and learn from each failure, you will end up with a desirable result over time.