Provide an accurate picture of the musical content - and if it's an unknown artist, perhaps refer to comparable musicians the reader might be more familiar with.

Don't provide an exhaustive list of track titles (Borinnngggg!)

Try to be dispassionate: if it's good say so, if it's poor, say so, without too much hyperbole (unless it really is fantastic or dreadful), and with reasons.

Know (or find out) something about the artist's previous career, for background and comparison.

Don't use the review to prove the cleverness of the reviewer.

Don't get such a bee in the bonnet about something incidental (cover design, liner notes, etc.) that comment on the actual music takes second place.

I probably fail on all counts several times per review, but no harm in having ideals.