I found that what helped me the most at CTAs is basically just "reps". Read a ton of them (which I'm sure you're doing).
But also: Keep in mind you have the benefit of "clinical correlation". If you know which vascular territory you're going to be looking at that also helps you hone into that area for the most part.
You need to be organized and develop a process for looking at images. For example I typically look at axials, followed by coronals, followed by sagittal images. I look at carotid—>MCA—>M3/small branches, starting at which side I think is symptomatic. Take a cursory look at the ACAs if the symptoms might be referable to that area. After the anterior circulation I look at PCAs followed by basilar artery down to the verts/PICAs. Then I’ll go down and look at the neck if there’s no LVO or high grade stenosis in the head.
You need to look at a ton of images and you need to have a process that you do not deviate from, especially as you’re getting comfortable with it. The time for this was training, but it is what it is and I commend you for trying to improve your skills.
Also, find a radiologist you trust during the day shift and go down to radiology and go through a patient’s scan with them. They’re generally very approachable and so long as you have a question they will go through the scan with you.