Main thing is to remove bloatware. That's sw that comes preloaded that you don't use or hardly use and starts up and runs all the time. Be careful not to remove something that you need to support the system. To remove sw, etc, use add/remove programs in control panel.
Then it depends on how much you want to update and keep sw current. When my computer starts up, besides the OS/sound/vid/etc, only wireless and antivirus loads up. This makes it boot fast. I don't need apple, etc searching for updates so disable all that and manually update when you feel like it. Or let it run, but the more things that look for updates etc, the more resources your computer will use. Common things that auto update are Antivirus sw, adobe stuff, os stuff, browsers, apple stuff, media players, blaotware/sw that comes loaded with laptop, etc...
The current norton anti virus is pretty good on memory.
Malwarebytes is good to have to check for viruses every so often.
VLC player is a great vid player.
Load other browsers like opera, firefox, etc and try them out. Whats good about this is you can have 2 instances of gmail, etc running from 2 different accounts. IE is pretty secure right now, but that changes and sometimes other browsers are more secure.
Loading too much junk on hd slows it down. Defrag every so often depending on how much junk you store on your hd. I do it once every 6 months or so because...
External HD are great for laptops. You always want around 20-30% free space on drives. Movies, pics, music, etc can be kept on externals when your main HD gets loaded up.
Most important is to keep your computer virus free. That will slow it down or worse, let someone into your computer.