It might help to think of things in a maturity model. Putting in a SEIM is a big job, and maybe more appropriate for when the security program at your org has matured more. What you can do is spend time working on the other stuff - what’s your endpoint protection? What compliance requirements do you have? How’s your inventory & asset management? What’s policy look like? Do your AD accounts all make sense? What’s the password policy? Do you have any old service accounts?
Picking little stuff allows you to make progress, and gets you ready to move to the bigger things. A mentor once told me to use a checklist (for life in general, but applies to cyber):
1 Did they ask you for help 2 Do you have it to give 3 Have you done enough for now