I made my best progress years ago deadlifting once a week, every Friday, 1 set to failure at the end of my workout.
Eventually, it did not take long, I was able to deadlift my entire York Olympic set (330 lbs?) for 20 reps. To put things
into perspective, at the time I weighed maybe 155lbs soaking wet.
For what it is worth, one thing I noticed, and others may have noticed this too, is that there is a direct correlation
between deadlifts and squats; meaning the more you can deadlift, the more you can squat. There seems to be a
symbiotic relationship / effect between the two. Though I was never much of a squatter, not for lack of desire or
practice (300 lbs once was about as good as it got), deads did help my squats.