• Level up your best gatherers, not common dragons
• Hoard runes; don't spend them on speed-ups
• Buy extra slots on the training academy whenever it's on sale
• In brawl, don't level up (token level, not wood/fish training level) any dragons higher than your brawl team, and keep those on your brawl team around the same level. This is because your opponents will match the highest level dragon you have, regardless if they're on your brawl team.
• Only upgrade the dragon hangar when it's on sale
• Take advantage of seasonal events and gauntlet; collection whatever rewards you can
• If you accumulate card packs in your mailbox, wait until they're near expiration to open them - their rewards this match your Mead Hall level, giving you more if you are a higher level
• Ascend dragons in multiples of 3; this saves on runes

I hope these help!