Image credit to:Shaad Boochoon
Once I have a steady blueprint with all the storytelling and gameplay set and ready. My next step would be to work on a prototype based on the said blueprint. This is the final chance to make any major changes to your design. Not to say it's impossible but it may be difficult
Do this part one feature at a time. Unless if each feature depends on another but try to avoid programming simultaneously to a minimum. Reason being that you might find yourself in a situation where you found that you have more than enough features. Maybe your game ended up becoming too complex from having too much features for the player and so on.
Program only the core feature and test it out. Remember, what you are doing here is just more of a proof-of-concept rather than something that will be used in the final game. If you are programming a shooter and trying to test out the AI you don't have to go in and start programming things like animation but rather things that players will be affected such as detection or pathfinding.
Speaking of animations it is important to keep in mind that you should not focus on art here. That comes later. Animations, textures, shaders and models are not important. Using a default cube or the default character model that comes with your game engine software is already good enough. Having the game just run with all the characters in T Pose throughout is something common in a prototype. You are working on the feature. Not the art style
And feel free to throw out anything that you found to be bad to your game Once you have decided what you want or don't want in your prototype you have basically created a very simple version of the game already!