When baking your cake try not to open the door, if you do then make sure you close it very gently to ensure you don’t knock air out of your cake and cause it to collapse.
When dealing with the cake mixture don’t bang the bowl as this will also knock air out of the mixture.
If making a Victoria sponge type cake ensure to beat the sugar and butter lots, until it is very light and fluffy, then gently fold in the flour.