Game architecture tips?

[humble tusk]

Hi guys,
I tend to see a lot of tutorials on specific subjects, but when i try to keep going onto a bigger project, i end up struggling/get lost into all my code.
Do you have any tips on general architecture of a game?

For example, right now, i'm trying to do a tower defense game based on a grid system. So i made a grid system which hold a node for each position with parameters such as is walkable, buildable, type of terrain and so on

Then i made a "contextual menu" to be able to build onto the node if it's buildable. It also handles the transition of the menu and so on. Then, it should display different options based on the actual node, if it's built, upgrading the building taking different building paths, if the player has unlocked this or that building, if the player has ressources to build it and so on

and yeah, i just end up being kind of lost into all my code and it gets messy