Before an interview
Anytime you have an interview, plan to spend at least twice the duration of the interview preparing. For example, when invited to an hour-long interview, prep for at least 2 hours. Here's what you'll need to do when prepping:

Research the company
Get to know the about, mission, vision and goals of the company! You'll want to know what their product(s) are, and identify why their product interests you. Familiarize yourself with their culture so you know what to wear for video or in-person interviews.

Research your interviewer(s)
If you have the name of your interviewer(s), go to LinkedIn and the company website to learn more about them. You'll want to prepare questions specific to your interviewer's expertise.

Know your value
Salary may come up as early as the first conversation with a company; be prepared for this question by researching market ranges on Glassdoor. More resources to prepare for this conversation here.

Brush up on your skills
Be ready to get grilled on any of the technical skills in the description. Set aside time to practice both your skills, and talking about them. For skills you lack, do research so you can at least speak about them with confidence.
Find more on prepping for technical interviews here and here.

Prepare questions
Always bring at least 2-3 questions to an interview space! Avoid asking questions you could easily answer with a Google search. Find some ideas here.

Plan for Murphy’s Law
Assume your bus will break down, traffic will be terrible, and that you’ll get lost on your way. Leave extra time for the worst-case scenario.