They are receptive to constructive criticism.

They follow through on what they say, such as offering to help out and following through with plans.

They are supportive of positive things.

They acknowledge any self destructive things you might be doing and offer support in addressing them.

None of these need to be 100% of the time because things come up and sometimes they can’t help you with every self destructive thing, but doing these things in general is a bunch of green flags.