A deliberately awful looking guide.

library(ggplot2)
data("mtcars")
str(mtcars)
## 'data.frame':    32 obs. of  11 variables:
##  $ mpg : num  21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ...
##  $ cyl : num  6 6 4 6 8 6 8 4 4 6 ...
##  $ disp: num  160 160 108 258 360 ...
##  $ hp  : num  110 110 93 110 175 105 245 62 95 123 ...
##  $ drat: num  3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
##  $ wt  : num  2.62 2.88 2.32 3.21 3.44 ...
##  $ qsec: num  16.5 17 18.6 19.4 17 ...
##  $ vs  : num  0 0 1 1 0 1 0 1 1 1 ...
##  $ am  : num  1 1 1 0 0 0 0 0 0 0 ...
##  $ gear: num  4 4 4 3 3 3 3 4 4 4 ...
##  $ carb: num  4 4 1 1 2 1 4 2 2 4 ...

I heartily recommend: http://www.cookbook-r.com/

g0 <-  ggplot( data = mtcars, 
              aes(y = mpg, x = as.factor(gear))
             ) +
      geom_boxplot()
g0

Notice I’ve forced gear to be a factor

g1 <-   ggplot( data = mtcars, aes(y = mpg, x = as.factor(gear))) + 
        geom_point(  aes(colour = as.factor(carb)))
g1

g2 <-   ggplot( data = mtcars, aes(y = mpg, x = as.factor(gear))) + 
        geom_point(  aes(colour = carb, jitter = 4))
g2

g3 <-   ggplot( data = mtcars, aes(y = mpg, x = as.factor(gear))) + 
        geom_point(aes(colour = as.factor(carb), size = wt)) 
g3

g4 <-   ggplot( data = mtcars, aes(y = mpg, x = as.factor(gear))) + 
        geom_jitter(position = position_jitter(),aes(colour = as.factor(carb), size = wt))
g4

Titles and themes

g5 <-   ggplot( data = mtcars, aes(y = mpg, x = as.factor(gear))) + 
  geom_point(aes(colour = as.factor(carb), size = wt)) +
  ggtitle("Red Main Title") + 
  ylab("Miles Per Gallon") + xlab("Number of Gears") +
  theme(
        plot.title   = element_text(lineheight=.8, face="bold", size = 25, colour = "Red"),
        axis.title.x = element_text(face="bold", size = 25,  colour = "#FF0055") ,
        axis.title.y = element_text(face="bold", size = 15) , 
        axis.text.x  = element_text(face="bold", size = 15,  colour = "Red") ,
        axis.text.y  = element_text(face="bold", size = 15) 
        ) +
  geom_hline(aes(yintercept=mean(mpg)), colour="#990000", linetype="dashed", size = 2, alpha = 0.3)
  
g5