Playing against bots (computer controlled enemies) can be good for practicing tactics and great fun for co-op style gameplay (friends vs bots). Unfortunately, Valve have not included any options screens to modify bot settings, leaving you with just the basic '5 on 5' gameplay. So, here are some of the console commands you can use to change the settings to suit your needs.
First of all you will need to enable the Developer Console, which will allow you to use the codes listed below. To do this, fire up the game, select HELP & OPTIONS and GAME SETTINGS. Here you will find a line labelled Enable Developer Console (~) - change it to Yes and click Back at the bottom.
Now you will be able to access the console by pushing the ¬` key.
(Note: The console can be assigned to a different key at the very bottom on the KEYBOARD/MOUSE settings page.)
Select PLAY from the main menu, and then PLAY WITH FRIENDS. You'll want to select a game type, so click GAME SETTINGS at the bottom, select CLASSIC CASUAL and finish up by select the map you would like to start with. It won't matter what set of maps you pick here, as there is a console command for changing the map to whichever you want (see below). Click GO when you are ready to start.
(Note: In order to keep the server between friends, change the server type from Public Match to Private Match.)
Here is a list of the console commands I have found and a brief description of each one. You must slide down the console (~) during gameplay and type these commands in.
mp_autoteambalance # - 0 or 1. Enables or disables the game's auto-balance feature. Required to be set to 0 for mp_limitteams to work. (Default is 1)
mp_limitteams # - Allows you to have # more players on one team than the other. Useful for stacking a lot of bots to one team.
mp_maxrounds ## - Sets the number of rounds you would like to play on each map. This is a 'best of' number, so setting it to 15 would require 8 winning rounds to finish the map.
bot_difficulty # - Sets the skill level of bots you are about to create. 0=easy, 1=normal, 2=hard, 3=expert. (Default is 1)
bot_add - Adds a bot to whichever team has the least players. bot_add_ct - Adds another bot to the CT team. bot_add_t - Adds another bot to the Terrorist team.
mp_friendlyfire # - 0 or 1. Enables or disables Friendly Fire (the ability to injure team mates).
changelevel ### - Allows you to change the map at any time. For example, changelevel de_dust. Type maps * into the console for a full list of available maps.
kick ### - Kicks a player or bot from your game. For example: kick togy. quit - The quickest way back to the Desktop.
(Edited 2015-07-16) bot_quota # - Used to set the number of bots in your game. Set 0 to disable bots completely (will stop them rejoining) or a higher number (up to 20 I believe, depending on the map) for more of a challenge.
This guide on how to modify bots in Counter-Strike: Global Offensive is by FlamingScreamer. If you have found it useful, please link to it.