1) Quit all other applications. The main issue that was slowing Audacity for me (and causing skipping) was my online backup software, which I eventually uninstalled. Some programs that might be slowing down Audacity may include a lot of the programs that appear in the "System Tray" for Windows users (in the task bar, near the clock). For example, you probably won't be needing instant messenger programs or the like while you're recording.
2) Beware of program automatic updates (such as Windows Update). They can make heavy demands on CPU or disk access at just the wrong time.
3) Turn Off Windows Firewall: Control Panel\System and Security\Windows Firewall\Customize Settings
4) Increase the Priority of Audacity: Windows 2000/XP/Vista/7 users can try Task Manager to increase the priority of Audacity once it has been launched. Access Task Manager by pressing CTRL + ALT + DEL, then click on the Processes tab. Select audacity.exe under "Image name", right-click over it and choose one of the priorities above normal. "Realtime" is not generally recommended. Try "Above normal" or "High". Sometimes, reducing the priority of any other programs you must run can help too.
5) Record to RAM. In Audacity, click: Edit, Preferences, Directories, then check the box that says"Audio cache". This will record to RAM (which is much faster than disk writing) then write to disk after recording finishes. Installing more RAM may help skips even if you don't use "Audio cache". To
6) Turn off "Auto-scroll while playing" on the Interface Preferences: ("Update display while playing" in Tracks Preferences in legacy Audacity 1.2.x). This stops the display re-drawing as the recording is made, freeing resources for recording. Alternatively minimise Audacity during the recording.
7) Try Restarting Computer: If you've tried all of the above suggestions but still experience skipping and slowing, try restarting your computer. Sometimes a fresh restart can close applications that were running in the background.