The L-Train is a nightmare at the best of times, but with all the changes coming up you will have noticed that it's gotten especially hairy (from April 26 and will continue to be so through Summer 2020). Here's what you need to know.
In short from MTA's official “L Project” page:
The revised approach for the L Project means that we'll be able to run service on the L at all times, with reduced service on nights and weekends. We've created an alternate service plan to help you navigate starting April 26, 2019 through summer 2020.
L-Train during your Weekday Commute
The best bit to note is that during the “busiest weekday times” (i.e. your daily commute starting from 5am), the L-Train will be running as normal.
L-Train After 8pm on Weekdays
The train service begins to “ramp down” with trains spacing out all the way to coming every 20 minutes in both directions at 9pm.
In Brooklyn, the trains will run more like every 10 minutes.
The trains will be running like night times, every 20 minutes in Manhattan and every 10 minutes in Brooklyn.
This is normal behavior for night times, but is more spaced out than you might be used to during the day.
Alternatives to the L-Train
Here's a great map on all the ways to get around without the L-Train: