startupsfromthebottom.com looks interesting! Do you come up with the ideas yourself, or what does your process look like?
What you describe (building a landing page or an MVP) is how most people do it. I would start even before that, since you should try to spend no more time than necessary on something that you don't even know is actually viable.
However, you obviously need to find out if potential customers are excited about your idea. In my experience, the following validation process works best:
* Write down a) the problem you're trying to solve and b) your solution. It's tempting to skip this step, but a lot of ideas may sound awesome while they're in your head, however that might change once you transform it from an abstract thought into 2–3 sentences. Try to be as succinct as possible while still capturing the core of your value proposition.
* Create a questionnaire based on your idea. Make sure to ask questions that are actually predictive of whether your idea might take off, such as "How often are you facing this problem" rather than "Have you ever faced this problem". Use a tool like SurveyMonkey or Typeform to put your survey online.
* Identify people in your target audience. This is hard. Don't simply email the survey link to your friends - because of something called "Interviewer bias", your friends & family will rate your ideas more favorably than an idea coming from some other anonymous source. Also, it's highly likely that your friends aren't actually in your target audience.
I run IdeaCheck.io[0], where we generate a questionnaire based on your idea and use a panel of respondents to gather direct feedback from your actual target audience. You can read more about IdeaCheck in my Indie Hackers interview[1].
[0] https://ideacheck.io
[1] https://www.indiehackers.com/businesses/ideacheck-io