It can be helpful to start the ideation process off slowly, beginning with a single idea rather than a whole collection. I for example think of an idea for 1, maybe 2, cards rather than think "I need to create a line of anniversary cards". Document your ideas process in a pretty notebook and do not get too bogged down with time or budget as these can be altered. It is also important not to write off your mistakes too quickly as you can learn from them.
If you did want to create a collection, then focus on a single element or concept to ensure that the collection is memorable without one item take the pride of place.
No single item will please all buyers which is why it is important to vary your items in purpose, price and production. Customers like variety which is why in Butterfly-Crafts I have complicated cards like Iris folding or Flowersoft and then more simpler cards such as Birthday cupcakes.
It is also important that a good number of your items require very little labour time otherwise the craft that you call your labour of love will soon become labourious.
Coming next time: Business Set Up Part 7 - Ideas Part 2