I've never seen a cut and dry best practice for tape labelling, but I'd say it depends very much on your individual situation, what your rotation is, what kind of drive / library you're using, who is doing the tapes changes etc.
For instance to pick two situations we have :
1) office environment, rotation consists of Monday to Thursday one tape each day, and then four Friday tapes, tapes being changed by random member of staff on-site. Label the tapes Monday, Tuesday, Wednesday, Thursday, Friday 1, Friday 2, Friday 3, Friday 4. The person changing the tapes just needs to keep track of which week they are on, other than that it's nice and easy for them.
2) Datacentre environment, rotation consists of one or more tapes per day, using a tape library which includes a bar code reader, tapes being changed by the ISP staff as you never generally see the physical servers. Use the bar code labels rather than a normal one, and get them to work out a rotation using the tapes provided (probably sequencially through the numbers). While it's more hassle for the operators, it does mean you can see exactly which tape was inserted easily, and therefore ensure that if an operator inserts the wrong tape on a day you need to do a restore from you can still tell them the exact tape you need (I've been caught by this several times with normal labels).
The key is to find a method which bests suits your needs, combining ease of changing tapes with ease of recovery in an emergency.
