I've been hoarding amulets and Shinwa items for a little while now. Drogon is over level 700 so I can only really fit a couple of training sessions in around my real-life work. Perhaps it's impatience on my part but to see any real improvement on the stats in a reasonable timeframe I think I want to just use the items as I retrieve them. What do you guys think? Also, is there a preference to items, or which ones should just be sold off?

Usually it’s best to wait until Tier 13, because EXP and Training Center costs are highest then, making boosters more cost-efficient. Doing Battle Quests every day is the real secret to earning a good amount of stats until T13. It doesn’t matter how far you get, just do as many as you can each day. It shouldn’t take more than 5-10 minutes.

If you do use boosters before T13, just be careful about items that boost level like tomes because they will balloon your pet’s level if you use too many at once. That makes the Training Center less efficient because course times and prices are determined by level.