You could do what I did and start at a little before "Crisis on Infinite Earths" (CoIE) and read every Batman and Batfamily book in publication order which is something like 4000 issues. It was worth it because Batman and the Batfamily often get the best writers. Also you get great things that you would otherwise never be recommended like Gotham Central, Gotham City Sirens, Harley Quinn's book, etc. You also don't get a complete picture of many of the more notable arcs like No Man's Land because they don't adequately compile it.
The problem with doing this is finding them all and keeping track because in the 90s you have 4 Batman books that released monthly along with several Bat-family books that released monthly often crossing over with each other.
I stopped reading after a year and a half of New52 because they had messed up a lot of the characters. They did not know what they were doing and were incredibly inconsistent about the timeline while saying nonsense that didn't work if you paid attention (which I did reading a lot of the New52 books to figure out the new canon and creating a timeline). At present DC is doing "Rebirth" which is changing the canon again, bring back the characters from the pre-new52 so it's probably better to read from CoIE.
batman: the killing joke which is a one shot and not part of the new 52
It actually is supposed to be
or the original series.
I am assuming you're talking about the Modern Era or Bronze Age which starts after CoIE, or slightly before.
Some recommend batman: year one
This one isn't part of new 52.
What you have to understand which you don't seem to is that comics have continuity but not at the same time. I'll try to explain...
When these comics started they all were part of one universe to some degree, but as time went on writers wanted to explore ideas that obviously didn't fit with the established characters so they just made them into alternate universes. Because of this there were now infinite universes...
Then in the Silver Age (i think the 60s) there was a reboot of sorts with a lot more sci-fi origin characters being introduced some which had the same name as the older character which led to the question of do they both exist in the same universe? The answer is that older versions exist in "Earth 2" and the New canon of comics exist in "Earth 1" but still "infinite Earths" which they can tell stories in.
In the 80s another soft reboot happened and it was considered that the whole infinite universe thing was too confusing so they did CoIE.
So at this point we have 30s-60s being one universe and 60s to 80s being another universe in 1 multiverse which was then smashed together creating 1 universe in 1 multiverse.
There were errors so some reboots happened which altered the single universe/Multiverse, but also at this time DC and Marvel worked together at times with Marvel more using the previous model which means we have a 2 Multiverses, the DC 1 having 1 Universe. I'm just mentioning this for completeness and it will come up again.
Then DC revived the idea of the multiverse and created a set number of universes, 52 to be exact and then later it was revealed that there is a multiverse of DC multiverses.. thus we now have Infinite Multiverses with Infinite DC Multiverses each with 52 universes...
And while this does change the timeline of a particular universe, technically all the previous timelines still happened in the ultimate universe so not actually ever a reboot...
That is the state before the New52. The new 52 rewrites the timeline and then collapses the DC multiverse, Variant universe, and Wildstorm universe together into a new DC Multiverse which is the new 52... but then the latest event happened and now we learned some things that makes the New 52 not that, but rather something else...
So where to begin? You could argue the very beginning, first issue, but pre-CoIE/Bronze Age/Modern Age there wasn't a lot to consider with canon and they are more like Episodic Episodes of a tv show where as after the Bronze Age become more Serial and so it is akin to asking where do you start in regards to a serial? at the beginning of that series/serial. In this case it is roughly CoIE. You can always just pick up where ever like a Soap Opera, but you'd be lost for a while and eventually you'd ask the same question and it depends on how dedicated you are.
To be honest though any Batman related book that doesn't have Batman in the title you can start from issue 1. The Batman books themselves are harder, but start with ones around CoIE and move forward from there...