library(ggplot2)
library(dplyr)
#Ordered by ggplot
df <- data.frame(Month = c("December", "January", "November", "February", "October",
"March", "September", "April", "August", "May", "July", "June"),
Value = 1:12, stringsAsFactors = FALSE)
ggplot(df, aes(Month, Value)) + geom_col()

#Ordered by Value
Ordered <- df[order(-df$Value), "Month"]
df2 <- df %>% mutate(Month = factor(Month, levels = Ordered, ordered = TRUE))
ggplot(df2, aes(Month, Value)) + geom_col()

#Ordered by Month
df3 <- df %>% mutate(Month = factor(Month,
levels = c("January", "February", "March", "April",
"May", "June", "July", "August",
"September", "October", "November", "December"),
ordered = TRUE))
ggplot(df3, aes(Month, Value)) + geom_col()

Created on 2019-07-16 by the reprex package (v0.2.1)