We are currently working now on improving this very same issue.
We plan to introduce various curated or predefined timelines including hashtag timelines for less experienced users. Advanced users will be able to customize or create completely new timelines with comprehensive filters. Either from following profiles, global, hashtag or pubkeys.
We already have list of suggested profiles to follow in Plebstr. I admit it has very narrow topics and it is not customised to specific areas of interest of each user.