Hello world!!
I’m starting game dev with a friend and we have a few cool ideas. But where do I start? I have most of my ideas layed out and a few 3d assets made but then what? Where do I start when I’m creating my game? Do i start with the UI? What do I do next?
Thanks in advance 
A common way to begin a new project is to get a very basic prototype working. Don’t worry too much yet about making things pretty, just get an object on the screen, allow the player to move it around, get your most basic game mechanic working and “fun” before spending too much time on polish.
Doing things that way also helps with motivation. Little wins, visible forward progress can really keep you going.
Great thanks but for my code, where do I start?
That’s a fairly open ended question. Do you know how to code? Do you know how to use Unity? Perhaps going through the tutorials in the Learn section linked at the top would be a good place to start.
I ALWAYS start with the map scenes… You should use your creativity on it first. Why? Because you need something to play before making a menu that allows you to, basically… open the air because you still do not have a ready scene.
I normally do this:
First, i write everything i want to do, so i don’t forgot what i want to make.
I make the TUTORIAL level.
Then i start making the other levels and maps untill half percent is done.
Then i start making the scripts AND to customize the maps with some “secrects of developer” to made it beautifull and nice.
Once the levels and the scripting are almost done, i start to make the main menu.
After the game is “playable”, i start to do the advanced things, such as cinematics, extras, etc…
Then you just need to adjust and add what is missing.
Try doing a tutorial (especially the roll a ball tutorial): Unity Learn
Then work on some concepts. Don’t try to make a whole game from the start, try making different aspects of your game in different scenes or projects.