In a first person story I am writing, I have many subplots going on, but when I started writing it, I realized that the subplots were not obvious. How can I make it more clear that progress is occurring to my subplots?
Don't worry about it in your first draft. Wait until your second, possibly your third. Your first draft is to get the story down on paper. Then you let it sit for a month and go back. The second draft is to fix all the glaring errors you pick up in your first review.
After a second (fourth, etc.) round, hand it off to a trusted reader. Ask the trusted reader after the reader is finished if the subplots were obvious enough. Take the reader's suggestions to beef them up.
This is an obstructed arborvision problem: you won't be able to see the forest for the trees, because it's your story and you know where all the plot threads are. You have to ask for outside opinions to get perspective.
You need to be very conscious of the difference between history and story. If you have multiple sub plots that are not obvious, there is a good chance that they are more history than story.
History is a bunch of stuff that happens. History consists of many things happening at the same time in independent threads, so you have to do some folding of time-lines in order to describe all the various threads.
But story is something very different. Story is like a bent bow. It is an arc of rising tension. Everything you tell should contribute to that arc of rising tensions. You don't follow the logic of history in telling a story. You follow the logic of tension. Sub plots should follow their own arc of rising tension, but should also in some way contribute to the rising tension of the main plot.
So, it does not actually matter that a subplot is not advancing in time sync with you main plot. What matters is, where does the insertion of the sub plot in the narrative contribute to the arc of rising tensions. If that means telling the sub plot out of sequence with the rest of the time line, that's fine.
The short answer is: don't worry about it.
The longer answer is: don't worry about it until the first and second draft are done and then don't worry about it because it is either a plot or not.
The truth is that it is very hard to gauge what the readers will pick up on. Some readers will pick up on your more subtle plots and others will miss them, this is healthy and normal. Don't underestimate readers - they will notice stuff you missed and miss stuff that you are justly proud of.
While writing the only question should be "am I telling the story?" After the story is written a really good writer's group or some trusted beta readers that you can interrogate about what they got out of it can help you gauge what readers might be able to pick up on.
If a subplot intersects the main plot and feels contrived to you then there might be a problem which you can fix in the next draft. However, if this is not happening - if you, as a writer, can follow the plots - then everything is actually fine and this is all just a mild case of imposter syndrome trying to derail you. The best cure is to not worry and get on with what you do best - telling your story.
If there are a lot of truly minor sub-sub-sub-plots then what you really have are details with ideas above their station (so don't worry about it).
If you have sub-plots that don't matter and have no bearing on the story what you may have is filler. You might end up removing that in later drafts but don't worry for now.
If your sub-plots are just really subtle then what you have are interlinked events that the reader might not see coming until it arrives. Congratulations you have written a great story (so don't worry).
As I said at the start: In short, try not to worry about it.