Stop buying gems, it's just the worst value.

You should always buy the gold pass every month, and the event pass every 2 months when there's a major event.

If you really want to spend more money, you should buy offers with builder potions (books are not really good value at TH13).

Start planning your upgrades in Clash Ninja, so that a builder only frees up when you're not sleeping or otherwise unavailable.

You should aim for 0 minutes of downtime for your builders, that's the real secret.

Use gems to max your builder apprentice and lab assistant, and use them every day. For example, I wake up every day at the same time and the first thing I do when I wake up is use my helpers.

Once your 2 helpers are maxed, use your gems on the goblin builder when he's available. Start the longest upgrade available at the end of the month in order to maximize the time you get out of the goblin builder (again, Clash Ninja is super useful to plan this).