Now that they have removed the HP from 3* and 4* covers, how do people earn their HP?
For me, it involves playing for a ranking in PVE and avoiding a shield if possible as these days an 8 hr shield is a net zero proposition, or getting by with a single 3hr.
The latest PvE gave me quite a bit. You could get 100 HP a day if you were in the top 10. When PvP has no rewards I really want, I can generally get top 15 without using shields.
Place in PvP events or dailey rewards. I tend to either get myself in a position for top 45 (fight for 15th or so with an hour or so left ans no shields). Thats the easiest way. I alternate between that and fighting for top 5 or 15 with shielding depending on the prize.
It allowed me to build my roster to 26 while staying competitive.
The long PVE events like Brotherhood are excellent for HP as long as you manage your MMR and rubberbanding. I was managing Top 5 and Top 10 most days with a non-amazing roster. The prologue has a bunch of HP in it as well, grab all of that. I am up to 17 slots without buying any HP, with more HP still sitting in the prologue waiting for me.
Placing in PvE events are the best way: in the previous event, placing top 5 in both subs got you 100HP a day. If the PvP tournament has rewards that you don’t need, placing top 45 will also get you 100HP if you don’t use shields (+50 from the prog awards). You need to be pretty hardcore about it if you want to actually net positive HP though.