2 buttons

#include <Servo.h>

const int  incSwitch = 8;
const int  decSwitch = 7;
const int  servoPin = 13;

int angle = 90;
int change = 2; // this value determines how much the angle changes each time through the loop

Servo servo;

void setup(){

 pinMode(incSwitch, INPUT);  // initialize pins
 pinMode(decSwitch, INPUT);

 digitalWrite(incSwitch, LOW); // set internal pull up resistors
 digitalWrite(decSwitch, LOW);

 servo.attach(servoPin);
}

void loop(){

 if( digitalRead(incSwitch) == HIGH) {
   // here if increment switch pressed
   angle = angle + change;
 }
 if( digitalRead(decSwitch) == HIGH) {
   // here if decrement switch pressed
   angle = angle - change;
 }
 angle = constrain(angle, 0, 180); // limit value of angle
 servo.write(angle);
 delay(20);
}