This is such a general post, I apologize for not knowing exactly what you are looking for here.
What is your dev background? You say it's your first time making a real game, does that mean you've made other games and just didn't commercially release them? Didn't release them at all? Were they just prototypes? Were they in a different engine? Or is this your first time using any kind of software to make a game?
Any advice someone on this forum would give you is going to need to know a little bit about what you know, so we can assume what you don't know.
Are you looking for just general tricks to speed up development? Or to minimize mistakes? Are you looking for advice on a certain aspect? Coding? Art? Where to find assets? How to make assets? Distribution?
If this is your first time making ANYTHING, you might want to do some micro-games first, find a YouTube tutorial series to follow along with while you learn the basics of the engine you want to use.
You say you are going to use Unity and both you and your friend are developers, does that mean game developers, software developers? What are your skill sets? If you want to use Unity you might want to invest some time into learning C#, though I believe they support visual scripting nowadays as well. Microsoft Learn has a lot of free C# resources to learn the basics of the language, by the end of that course you should be able to read documentation, which is the key to being able to program a game, documentation being the specifics of the Unity engine, so that you can use C# to control aspects of it.
Please give a little more context as to what part of development you want advice for and I, and I'm sure others on the forum would love to help with what we can!
Best of luck!