There are lot of secure option for Windows, You can secure by -

Set a difficult password for administrator

Disable gust account

Give minimum & limit permissions to administrator's members

Make minimum share folder on your Windows's

Give minimum share permission on that folder & full control to trust users

Always change the administrator password

Install third part firewall & set minimum port.

Access & deny those user's & IP which you don't want to access to your computer.

Don't share your password.