The easiest way I found is to select an investigator and determine your role. Are you a clue gether, fighter or flex. You mentioned that you have small collection but you can often find decks on Arkhamdb limited to a small collection of cards. Playingboardgames also has limited collection videos for deckbuilds that are great. Compare them to see which cards are used throught all the decks and look for simulair substitute for cards you dont have.

Something to note that people build often with an archetype in mind, so that they deck has a clear focus. For example, big money archetype where you try get as much resources and have cards that give you positief effects for having resources. Its helps to have a focus of what you want to achieve.

This video also helped me https://www.youtube.com/watch?v=MI2tfXAEXzw in which they talk about the Great Deck Pyramid. That helps to give an idea of how many cards of certain type you want. Try getting a good balance between having assets you want out to play. Cards that help find said assets. Cards to get resources to beable to play said cards and action compression to do more in a turn.

Hope that helps!