Tips to grow stronger

Upgrade other buildings first

While rushing to upgrade your Stronghold as soon as possible is nice, as it often unlocks new shit and rewards, there is also something to be said for first upgrading the majority of your other buildings.
First strengthening what you already have, will keep your resources low —making you less of a target— while giving you more time to accumulate the unlootable resource items instead. It also gives you time to accumulate a larger troop count, which will help you gather more resources, more quickly.Make sure at least your city farms/sawmills are fully upgraded.

Instant Yield Talent

Get the 'Instant Yield' Talent if you haven't already. Before you use it every 12 hours, make sure you have used your 24h farm/mill/mine boosters as, as far as I know, they will increase the instant yield too.
Try to use at least 2 farm and sawmill boosters every day for the Daily Activity Points for your Daily Rewards.

Don't use your resource items till you actually need to.

Why? Because otherwise they can be stolen, and, in the case of food, anything above your storehouse limit will be eaten up by your troops upkeep cost anyway.Which is also why collecting food should be your last upgrade gathering priority. First collect the required wood, ore and silver, then start gathering the remaining food you need. Consider using an upkeep reducer item as soon as you have a nice load above your storehouse limit.
One exception perhaps: try to use at least 5 resource items every day to collect the Daily Activity Points for the Daily Rewards.

Hunting Monsters and Rallying Barbarian Camps

Raid camps and hunt monsters when you can. They are excellent sources of resource items. If I recall correctly, a level 15 (or 16?) cyclops has a nice chance of dropping 45 x 1k food or wood resource items. This really adds up quickly. Especially if you take your time to grow your troops and get the Monster Stamina Talent.

Monster Stamina Talent

Once you have the Monster Stamina Talent (reduces stamina cost by (iirc) 20% for 10 minutes, with a cooldown of 24 hours), save up a full stamina bar, activate it, and try to deplete your stamina in 10 minutes.
Use a full march of your primary troops to attack the strongest monster(s) you can, while using your secondary (and possibly tertiary) troops to kill the highest of a stamina tier that makes most sense economically.Before activating the talent, consider bookmarking monsters that you can't use the Hunt tool on, so you don't waste your timer scouring the map for monsters of a specific tier.

Gold Events

Gold Events are a great way to get items and gold, and a nice extra incentive to strengthen your power. Try timing them so you start earning points already directly as soon as the game day starts at midnight UTC.

Monster Kill Stage

If the next day is monster kill stage of gold event, make sure you start the game day (midnight UTC) with a full stamina bar and your monster stamina skill ready. Save up your Stamina refill, and march speed items. Consider using a Attack Boost and/or March Capacity Boost item, so you can take on monsters that are stronger than you can usually kill.

Upgrade / Lord Power Stage

Time two upgrades which increase the largest amount of hero power to finish directly as soon as the day starts. Especially awesome if you can plan your SH upgrade for that. Don't accidentally insta-finish too soon though. ;-)
Save up some of your timer speed-ups to use in case you run out of time, or if you want to rise a couple more ranks. It helps to have plenty of resources available for this stage as well.

Troop Training Stage

Plan a full load of all your troop types to be done at start of game day, and collect them as soon as the event starts. Also time collecting the last load of finished troops just before the event day ends.
It's important to note though that points aren't awarded when they finish, but rather when you collect them! So, learn from my mistake, lol, and don't forget to collect them in time!
Again, remember you can use timer speedup items to get more troops done in the limited amount of time. Consider buying some more speedups with gold, if that will mean collecting the reward for completing the last tier of the gold event stage!Finally, don't forget that you don't have to build a full load of troops; you can drag the amount slider in a way so the timer will match how long you still have before the event ends (or before you have to log off because you have to go somewhere, so you can start a fresh, full load right before then).

Gather Event Stage

Plan your gathering troops to return as the event starts, and pull them back again right before event day ends, even when they haven't loaded up fully yet. Important to note is that points are awardedas soon as they start returning,notwhen they have returned to your Stronghold.

Remember to use a 24h gathering boost as soon as the day starts. Try to gather with your primary troops at your Alliance Farm/Sawmill/Iron Mine/Silver Mine as you get an additional gathering boost there. Note that Siege Troops have the highest troop load.

Aim for the highest level resource sources, as they contain the most resources and thus reduce the time wasted on marching back and forth. Make sure you gather at a full resource location, not one that's already half-depleted. Send out as many marches as you can. If you have less troops than you can fully fill marches, but a full march would be able to carry more resources than the farm/sawmill/mine has, consider matching the march troop load to the resource source capacity. They might stay out longer than using your full march, but if it means being able to send out another concurrent gathering troop, the reduced march time might be worth it.

Be sure to check out the Gather Event Stage section of the Gold Event page for more tips.

Alliance Storehouse

If you alliance has an Alliance Storehouse, you can keep some of your resources safe by sending them to the Alliance Storehouse. Every day you can send a maximum amount to it, up to a general limit. Note that the daily limit is store-only; taking stuff out won't reimburse some of that limit.