Hi! For sleep if using whole flower you should find a tested product that is pesticide free and that the dispensary staff can show you the cannabinoid and terpene profile and explain to you why the higher concentrations of certain sedating terpenes are why they are showing you a particular flower or vape oil for sleep.
If using an edible or tincture remember that 5mg of THC is a starting dose for new patients and you can work your way up from there by 2.5 or 5 mgs at a time.
Remember that CBD promotes wakefulness as seen in this and other papers and isn't going to make you sleepy all by itself.
However, if you prefer a CBD rich formula, their is research where patients reported improved sleep when using a 1:1 ratio :) Likely because there is enough THC in a 1:1 to still make you sleepy.