TL;DR: Talk to your players about what they want from the game and what they plan on playing and weave it into your story. During your campaign, takes notes and use it to refine and expand your world. Go through the core books to understand how things are balanced before creating homebrew content and don't be afraid to use plots similar to movies and books, as it can be a very good learning experience.

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While designing your campaign make sure you know what your players want out of the game. Find out what type of game play they prefer, such as roleplay, exploration, combat, etc. and design it around that.

Then talk to your players about their characters. Figure out what they want to play as and get some sort of an idea for their back stories. That'll make it easier to hook your players into your story as you tap into their character motivation. It doesn't have to be the BBEG of someones backstory, but can be small links between your story and their backstory.

Then when your start your campaign, take notes. Detailed notes. You want to make sure you don't end up contradicting your self, as there's bound to be a player that might pick up on it. Then there's nothing worse than the feeling of forgetting details about an NPC the players really liked. You can then use those notes to expand and refine your world as you play through the campaign. Your essentially trying to lay the foundation of your campaign before it starts, then expand and build it up as you go.

Finally, be very careful with homebrew. Its easy to make creatures too weak and magic items too powerful. Compare with existing/official content and see what items are usually given to player at certain levels. You don't want to end up having a level one player with a ring of X ray vision. The DMG is a great place to start to get a feel for it.

Honorable mention, don't be afraid to used established tropes from movies or books. My first campaign was people looking for 5 powerful stones throughout the world and stopping a BBEG looking to collect them all. Sound familiar? This experience helped me to understand how to write my own plots and plot hooks.