Macarons are already finicky. Do not try making substitutions. Also, find a high quality recipe that walks you through the steps with visual indicators.
Measuring by weight is really the only way to get the same amount of each ingredient every single time! Invest in a kitchen scale when making macarons.
Air bubbles can form in the macaron shells simply from the mixing and piping process. To fix this, gently tap the sheet pan on the counter & pop with a toothpick.
The macarons need to sit for around 30 minutes until they develop a "skin". Lack of allowing the macarons to dry long enough will result in cracked shells.
It's best to allow your macarons to sit in the fridge overnight with the filling. This allows the macaron to slightly soften and develop a deeper flavor.