You can do some smoothing like this:
float newAngle = 3.14159265 - (LDR / 325,6310);
#define ALPHA = 0.2;
static float angle = ALPHA * newAngle + (1-ALPHA ) * angle; // changes smoothly to new value, speed depends on ALPHA
int x = 90 + 65 * cos(angle);
int y = 490 + 65 * sin(angle);
line (90,490, x, y);
OR average multiple readings (takes more time)
int LDR = 0;
#define NR_LDR_READS 4
for (uint8_t i =0; i< NR_LDR_READS; i++) LDR += analogRead(LDRPIN);
LDR /= NR_LDR_READS;
etc.