Here you can find some building tips.
Guide to Build Base
Expansion is key, especially since gold tends to be rather critical through out and homes do not provide a great deal of gold, locating even a small vein of gold can give you a 150-300 gold boost and the very large veins nearer the edges of the map can give upwards 500+ with just the basic quarry which makes a world of difference.
You need to make layered defences, basic at first along areas not expecting a crystal wave (usually gate, wall and a tower with 2 archers, changed to a single balllista once they are unlocked and you have the spare gold).
Along areas expecting to hold back a wave you’ll go for layered defence even more, wall, aoe flame tower, wall ballistas/towers, wall, aoer flame tower again, wall, balllista’s/towers again. This is especially useful once you get to death wave 3 where you can some rather… nasty things come for you.
Each layer of wall has a space in front of it along with gates so you can send in sentinels/flamers to help hold the enemy back, flamers especially, while allowing them to retreat when they are close to death. In essence you’ll work to bleed the enemy while expecting at least 2 layers of defence to fall. Ideally you will get rid of any nasty enemies using towers to target them specifically (would be great to have target priority but hey oh work with what you got.)
Since defensive structures don’t cost any thing other then villagers they can be left at your choosing though reduced along areas where you won’t have a death wave.
As to general building, you need to have a wood work shop up by day two ideally along with a training hall to start producing troops, since farms area vital early game research, that and having the keep upgraded by day 3 for the additional gold income.
One key note is to be very sure where a wave will head, you have a few cases where a wave which you though was going one direction has gone down another fork in the road and bypassed defences as a result. So ideally always have sight on the crystal and near by areas to ensure you know what path they will take. It helps if you have alarge stockpile to build emergency defences if required.
Also side note, always build storage buildings next to quarries, it gives a 2x boost to their gathering rate. They had a radius of effect that was view able but well it works for me atm.