N = 100

XX = rnorm(N)
YY = rnorm(N)
Condition = rep(c("red", "blue"), N)

dd <- data.frame(x=XX, y=YY, c=Condition)

extremes = max(c(abs(XX), abs(YY)))

library(ggplot2)

p <- ggplot(dd, aes(x=x, y=y, color=Condition, shape=Condition)) + 
	geom_point(alpha=.6) +
	ggtitle("Good title") +
	scale_x_continuous(name="x-axis", limits=c(-extremes,extremes)) +
	scale_y_continuous(name="y-axis", limits=c(-extremes,extremes)) 

#ggsave(filename="~/Desktop/plot1.png", plot=p, width=12, height=10)
#ggsave(filename="~/Desktop/plot2.png", plot=p, width=4, height=3.3)
ggsave(filename="~/Desktop/plotsize/plot1.png", plot=p, width=6, height=5)
ggsave(filename="~/Desktop/plotsize/plot2.png", plot=p, width=4, height=5/2)