Dignfight Strategies

You're given 20 sapphires to begin with. Some of the bonuses are definitely worth it, but unless you intend to buy more sapphires, you had better spend them wisely.

Burning Eye: Only worth it if you've purchased additional sapphires. The +10 bonus in carrying is the only thing that I care about...naturally, I concentrate on digging and currently have level 10 Imps.
If you've purchased sapphires, keep Burning Eye active ALL the time.

Moldy First-Aid Kit: Only worth it if you've purchased additional sapphires. Saving half of your healing costs is awesome, BUT there are better things to spend your 20 sapphires on.
If you've purchased sapphires and if attacking is a prime part of your strategy, you will want this premium active at all times.

Home Training Made Easy: Very tempting premium. If you have a lot of training spots, this is the 2nd most valuable premium to use.
If you've purchased sapphires and you have 12 training spots, make sure that this is active each time you begin training a unit.

Ring of Flirtation: Only worthwhile if you're doing a LOT of recruiting. Grabbing 12 Dark Riders will only save you 5760 gold. Compare that to Home Training: 12 level 1 Dark Riders + Home Training premium = savings of 4320 gold (and twice that amount to train all 12 from level 2 to level 3).

Hammer of the Handyman: Here is the number 1 premium for most players. Save 5-10 sapphires until you are ready to upgrade your Arena to get Dark Riders. This will save you at least 1000 gold per upgrade AND with the discount, you don't have to sit around with your pile of gold for as long.
With a decent team of Imps, it will probably take you 2 weeks to move from a 4x4 Guard-room to 9x9.

Talisman of Greed: I've never used this one, it just doesn't look very useful. If anybody has a different opinion/experience on this one, let me know.