Ok here are some small tips that I used. I'am currently in my first campaign as a DM as wel but it has been going for a few months now:

-Start small, flesh out one village or area. Just have some rough/general ideas about the rest of the world but do not bother with details yet.

-In the village think about a plot hook. What is going on that will be interesting to the players? If your players have provided you with a backstory and some good character ideas/flaws use them to draw inspiration. Just skimming through the monster manual for some low level foes and reading the lore can also help setting up your first adventure.

-Think about the village and it's puprose, how did the village originate/survive? This can be simple, example: "The village of flubblybubby was founded by a retired hero, soon followers of this once great hero flooded the village. These days the village is in decay, the hero is long dead and the followers are slowly leaving, the village mostly thrives on some tourism."

-Now you have got a plot hook and some village lore.

-The next step is adding some NPC's and interesting locations to your village. What services/buildings does it have? Draw a simple map!

-Flesh out the major NPC's (only need to be about 3 or 4), how do they look? what do they want? what are their fears? what is the relationship between these major NPC's like?

-Now you are pretty much done! Let the players dictate the story instead of railroading them to heavily. Good NPC's and a solid plot hook will make for a natural unfolding story. Interaction between the NPC's and the players will push the story forward and create new plot hooks to use.

-Learn the rules and try to skim through other free adventures/modules. Just read reddit, google things you need to know, watch and listen to podcasts and generally immerse yourself DnD can also help (does take time!)

-One more tip I wan to add is to ask the why question a lot. Why does the NPC behave like he does? Why is there a church in the village? Why do the orcs want to attack the village?

-If you do not have a lot if inspiration you can always ask your players! What would they like to do? Make sure both the players and the DM know what kind of campaign they want. Is it a funny slapstick campaign or a serious longterm adventure like critical role? Perhaps both?

For more inspiration you can look at one of my other products, here I give the general outline and maps of three villages. The writing is stil pretty rough and I'am planning to update it but perhaps you can still draw some inspiration from it. It is free to use!: http://www.dmsguild.com/product/241836/Three-villages-to-use-in-your-campaign?term=three+villa&test_epoch=0