I prefer to warm my almond milk and add a flavour before use. Here’s what I do.
Warm the milk with vanilla essence or extract over a low flame for about 5 mins.
Do not leave it unattended. The milk should just be warmed and not left to boil. Boiling makes the milk curdle. You may also sweeten your milk if you like. I don’t sweeten my almond milk because I usually add cereal and dried fruits to mine and get the natural sweetness from the fruits instead.