I don't find that I am pushed into the Modern UI - I rarely see it, except after rebooting, and when I deliberately call it up. I have never used a start menu replacement either.
1. on the Modern UI Make sure that Desktop is at the top left tile - that is the key start tile (just like reading English text) - press enter on start, and it takes you to desktop. Windows 8.1 will make this superfluous.
2. use a local logon - you can use a live ID to activate any tiles you need to - if you don't want to log in all the time, use netplwiz to set up autologon, and disable password for wakeup on the power control panel and screensaver on personization if necessary. Keep UAC on, but set yourself up as an administrator, and not a user, unless you cannot trust yourself.
3. unpin /uninstall tiles you are never going to use (keep the store though, just in case) Unpin all those tiles from any desktop applications that you only run from desktop icons. When (desktop) Setup and Install programs offer to put shortcuts everywhere, only check the shortcut on the desktop. Unpin their tiles from the modern UI as necessary. Pin your everyday shortcuts to the taskbar.
4. hide your desktop icons if you want a tidy, quick desktop, and never put anything on the desktop unless it is a shortcut. Use the Desktop toolbar in the taskbar to access desktop shortcuts.
5. Shut down using the power button and use the hybrid boot feature or sleep instead of rebooting all the time. Set your usual preferences in the power control panel applet. Only do a full shutdown to reboot when Updates are installed at a time convenient to yourself, like when you are going off to eat or to the shops etc.
6. Wherever possible keep the Windows defaults for an easy life - I rarely use Internet Explorer, but it is set as the default browser, so that any malware I may pick up goes there instead of Chrome which I use all the time from a button pinned to the taskbar. Use the Windows Firewall and Windows Defender, but also have Malwarebytes for occasional cleanups. Don't stuff your system with 3rd party utilities - defraggers, registry cleaners, partition managers, driver updaters, desktop enhancements and so on - they probably will eventually stuff your Windows up, whatever they promise.
7. Only use webmail that you can read in your browser - Microsoft Outlook, Live, or Hotmail as was, Gmail, Yahoo, your own ISP's mail - do not use a mail reader application on your PC - you will pick up infections.
8. learn the hotkeys and keyboard shortcuts
9. keep a written record of passwords, product ids and application installations, and if you throw out old install disks etc burn a copy of the software and keep it on some free cloud storage and note down where the files are and what they are called together with the passwords.
10. Ask questions to problems here, on eightforums.com, however simple or silly you may think them to be. You may be helping someone else out too, because your questions and answers get onto google within hours, and there is a mass of knowhow here.