Practicing alone
Everytime you run QuakeWorld, there's the option to play by yourself, practice movement or aim, alone or against bots.
You can do it on a public server (look here), or you can run your own server on the same computer you play (see How to server.
Aim
Aim maps are usually played in Deathmatchmode4 (most commonly known as dmm4), where you get full health and weapons. Popular maps are povdmm4, end, end2, amphi, among many others. Midair is a slightly different mode, where you only have rocket and frags are done only by hitting your opponent in the air. Popular maps are midair and Endif.
On KTX servers, the recommended map settings are loaded when the map is loaded, so you only have to vote on the map, and type /ready to start playing immediately.
Movement
versus Monsters
see Bloodfest.
Bots
Bots replace human players. You can spawn bots in compatible KTX servers. See more Playing with bots. In the past, bots required a specific modification, popular ones were Omnicron and Frogbots. You can also try Humanoid.