Batteries such as in the iPhone don't have a memory effect.
Meaning if you use them till 30% everyday then recharge them, they will NOT soon retain only 70% of their original capacity. Thus no need to use them till near 0%.
That said, the first couple of cycles should be complete charge/discharge every time in one go to calibrate the charging.
I usually recommend to my clients to charge it till full; then use it till near 0% in one go, then charge it till full also in one go.
To extend the life of your battery, avoid exposure to high temperatures, use of cheap chargers.
When storing for a long time, battery should be 50% full.
Finally, the lifecycle of a battery is usually in cycles. 1 cycle is 1 charge from 0% to 100%, then discharge back to 0% or vice-versa.
Some say that they keep the count of cycles low by keeping their device connected to a charger. This is not good and will also deteriorate the battery because in these types of batteries, electrons must keep flowing meaning the battery should be cycled normally, not kept connected to a charger.
I am not a battery expert. I researched this subject and the above is a summary of information I found by reading articles (not opinions) in various places; among them what Apple themselves had to say about their batteries.