Great question!
First and foremost, try to avoid games that are "asset heavy": RPGs, RTS, MMOs, Metroidvanias, CCGs, SIMs, MOBAs, Adventure Games, Management/Tycoon games. Also avoid multiplayer or networked games, anything requiring good AI, and specialty equipment like ARGS or VR. If this is your first game, I also recommend AVOIDING a game with an explicit story (unless you are doing a text/graphics-based interactive novel game in Twine or Ren-Py where the whole game IS a story. In which case, keep it BRIEF). If you do include a story, the entire script should be readable in under 3mins.
Instead, focus on games that are more "system" focused: Puzzles, board/dice/solitaire, simple shooters, platformers, casino games, simple physics games (angry birds/flappy bird/breakout), tower defense, music/rhythm, simple farming, infinite runners, beat-em ups, and physics-based sports (bowling, golf, pool).
I recommend making an explicit schedule (I make one in Google spreadsheets). Make sure you factor in things like people's jobs/schooling, sleep, and other life requirements to figure out how many hours you have available for development. Then, cut the number of available hours in HALF. You want to plan as if you were making a game in just the first 2-3 days, then let the rest of the time be for bug fixes, polish, testing, menus, tutorial creation, sudden life requirements, and coverage for under-estimating how long something will take you.
Split your time between Design/Level Design, Coding, Art, and SFX/Music. But schedule more time for coding and things you are weaker on and try to minimize the impact of stuff you don't know how to do or don't care about. (Eg: Don't make a music game if you don't know how (or care about learning) to write music.)
IF YOU HAVE A TEAM:
Factor in extra time for communication. Make sure your team agrees on how to stay in contact (email, Discord, Texts, etc). I recommend having someone in charge of setting up a Trello board that breaks down everyone's tasks. Also be sure to setup an agreed upon way to easily share files (Dropbox, GitHub, etc). If you have dedicated teammates for assets (art/sound/music) obviously they will make the assets, but the designer/producer needs to help them breakdown how much time to spend on each asset or level.
IF YOU ARE GOING SOLO:
I'd recommend dedicating 4hrs on design, 2 days on coding/dev, 12hrs on art, and 6hrs on sound. If your game needs dialog writing, databases, or level design work; add another 2-4 hours for each.
EITHER WAY:
Consider your personal/team's strengths and weaknesses. If you are an artist or art-heavy team, you'll probably need MUCH longer to figure out the code than to pump out assets - so your game should be extremely simple and pretty. If you are a coder/code-heavy team, you may want to focus on a creating cool mechanics and reduce your art to basic shapes with fun shaders.
Good luck!