One of the most common causes of crashes when a new RC pilot is starting out in the hobby are control surfaces that are going the opposite direction they should for normal operation. It's quite common for some servos needing to be reversed for proper direction of the control surface when building a new aircraft.
How do I know which direction is correct given my stick inputs?
Here's how to make sure that each control surface moves in the right direction when you move the corresponding control stick on your radio transmitter. When you are on the field, stand behind your airplane:
To check proper elevator direction (P1)
When you pull back the elevator stick (the right side stick that controls aileron and elevator) towards you, the elevator of the aircraft will move upwards. When you push your elevator stick away from you, the plane's elevator will move downwards.
To check for proper rudder direction (P2)
When you push the rudder stick (the left side stick which controls throttle and rudder) to the right, your aircraft's rudder will move to the right of center. Conversely, your aircraft's rudder moves to the left of center when you push your rudder stick to the left and .
To check proper aileron direction (P3)
When you move your aileron stick (the right side stick that controls aileron and elevator) to the right, the aileron on the right side of your aircraft will move up, while the aileron on the left side will move down. When you move your aileron stick to the left, the aileron on the left side of your aircraft will move up, and the aileron on the right side will move down.
Here's a diagram for your reference:
