I know a few folks who are diving into new ideas. One way of starting up has been fleshing out the Lean Canvas — a simple one-pager in lieu of a business plan. 
Like a business plan, the Lean Canvas helps folks capture the key elements of a business without building out a detailed, largely never-to-be-used-again business plan. It’s certainly a good way to get started while thinking holistically. 
Another method I’ve been thinking about after reviewing “landing page how-to’s“(see Julian’s Landing Pages handbook) is what I’ll refer to as the Alternatives-Value-Personas (AVP) framework. This is a stripped-down version of a Lean Canvas. In fact, this may be a preceding model before the Canvas. 
(Source: https://www.julian.com/guide/growth/landing-pages) 
In this framework, the idea is to dig into the pain today — what exists — and describe the value of a proposed solution as well as the people involved. Why I bring this up as another option is to understand the problem and the people greater while having a hypothesis of the value of the solution. The most important facet of starting out a business is the market and the pain. Is there a pain at all? What exists solving the pain, or even contributing to the pain? 
Another option for folks is building on a Simplified One-Page Strategic Plan as David Cummings calls it. This is an outline layout of the key aspects of the business. You’ll recognize here, too, the template has specific sections for values, purpose, promise — cultural elements.   
(Source: https://davidcummings.org/2016/11/29/2017-simplified-one-page-strategic-plan/)  
There are a lot of different options to get started. However, the most important piece is understanding the audience and addressing real pain, or as one VC describes “hair on fire“.