I'd like to highlight something ShibuyaCloth said:
The golden rule/strategy of the Royal Exchange Trade is to flush your inventory overflow. Only use the Exchange to keep resources below the 99 inventory cap. If you find that you never have enough items in your inventory to kick off a trade, then you're potentially hobbling your ability to do quests and then you're just constantly playing catch up.
(As a an additional note, you may want to keep some items like Fur, Jewels and Glimmerdust below 90 so that your Kingdom trading partners can have the option to gift them to you.)
I alternate the trades of:
- Eggs & Dairy Exchange (40 Milk, 25 Eggs - 2Hr trade) - It only uses 65 energy to collect them, and less if you have 2 Stables and 2 Hatcheries.
- Meat Delivery (25 Roast Chicken, 25 Bacon, 25 Fish - 2Hr trade) - You'll end up spending more than 75 energy to obtain these items since Roast Chicken drops randomly (from Chickens and Hatcheries), and Fish don't always drop 100% from Ponds and Wells.
And when my inventory of Cow Hides, Wool and Fur each reach 90, I then do:
- Trapper Trade (30 Hide, 15 Wool, 15 Fur - 4hr trade) - I usually let Wool and Fur Max out while waiting for the number of Hides reach 90.
When Troll Horns, Creep Tooth and Bones inventory each reach 90, I then do:
- Troll Hunter Trade (20 Troll Horns, 20 Creep Tooth, 20 Bones - 6Hr trade)
I occasionally, but never usually do:
- Magic Fruit Trade (60 Strawberries, 40 Glimmerbulbs, 6 Magic Fruit - 4Hr Trade <--requires 106 energy to obtain resources only just to get 15 energy back) - The return ratio on this Trade is absolutely ridiculous. You can only get 1 Magic Fruit per day from your Magic Garden, and after you spend all that energy to get the ingredients, you only get 15 energy back. Once I stopped doing this trade, I found I had more time (and energy) to devote towards completing quests in my questlog. You're better off collecting milk and eggs than doing this trade.
- Trade with Belladonna (15 Living Wood, 30 Mushroom, 15 Rat Tails - 5hr trade) - Living Wood is too precious to waste on this trade. I reserve the use of Living Wood for Ornate Beams when my Living Wood inventory hits 90.
- Jeweler's Trade (40 Water, 30 Glimmerdust, 30 Jewels - 3Hr trade) - To get all those resources requires using at least 100 energy. I would rather use the Glimmerdust towards Enchanted Essences and Super Glue. Jewels are absolutely necessary for Royal Beams/Blocks.
I never do:
- Delicious Trade (2 Apple Pies, 2 Orange Cobbler, 2 Lemonade - 8Hr trade) - It's not worth the effort to gather all the ingredients, tie up my kitchens with cooking/baking, and then have the Royal Exchange building tied up for 8 hours for just 1 Gem.
- Golden Trade (3 Golden Nuggets, 2 Golden Eggs, 1 Golden Apple - 10Hr trade) - Hoard your Golden items. Unless you have an obscene amount of these in your inventory, you're better off holding onto Golden items. Golden Nuggets and Golden Eggs are used in some building upgrades. Golden Nuggets have been known to be needed for some quests. If you really need gems, just do quests through your Castle daily. The quests have a chance to drop 0-8 Gems per adventure.
- Trade the Fruit Farmers (50 Mushroom, 25 Truffles, 5 Magic Fruit - 2Hr Trade) - I have never found a good reason to do this trade except to just finish the non-core quest that unlocks it.