Placement is the key.
Backhauls is the other factor.
Ideally you want each AP to have a ethernet backhaul to your router/switch. Otherwise they become repeaters and have to rebroadcast back to the main router. (edit and thus halves their speed and doubles latency)
Unless you are using newer routers with more power and decent wifi? You will be better served by using proper APs like Ubiquiti or such. They are more powerful and designed for handling large amounts of traffic.
I personally use a main router (wifi disabled) and an AC-Lite AP. I get far better coverage and much better signal.