Rewarding Talent – Handbook on stock options for European entrepreneurs
indexventures.com
indexventures.com
That said, their suggestion of "Seriously consider back-loaded vesting schedules" is employee unfriendly (https://www.indexventures.com/blog/rewarding-talent-quick-gu..., tip 5)
In particular the idea of a 10/20/30/40 vesting schedule is non-standard, except maybe at places like Amazon. IMHO, if you want to retain people longer, use additional refresh grants instead.
Unless your in an EMI scheme which is only for companies smaller than < £30mill - which is the absolute Gold standard no income tax and only taxed at 10% - though the one I am in is rare in offering it to all employees.