Maintain small network where you only dealing with 3 or 4 computer plus a few (around 4 laptop that use wireless connection) machines is simple. Just plug the ADSL modem and turn on dhcp with default setting but when happy problem came (grow bigger to thousand computer) then its no more room for playing 🙂
Yes, most of past problem is came with cable. Good network design without good network cable is like building sandbox. Looks strong but weak inside. Last week we have a job to see a hospital network built by someone that heavily use network cable here and there. You can drying clothes with the cable due to the way they pull the cord.
After look around for almost an hour we came with conclusion, mainly judge old cable they use. We give them online reference too (related to price and youtube videos). Some of them listed here :
Use different colour
By using different colour you can easily identify which cable work as backbone and which cable work as branch, channeled to the client.
Blue cable for backbone and other for client. 
You might want to know if other colours is exist :
- White cat 6 network cable
- Green cat 6 network cable
- Black cat 6 network cable
- Gray cat 6 network cable
- Red cat 6 network cable
- Yellow cat 6 network cable
Use cable connector
Use connector when needed and never twist it roughly. I see very brutal connecting cables such as power cables twisted way. There are many cat 6 connector available with colour options too (black, blue, gray, green, orange, purple, red, white and yellow).
Use specific Jack
When need to combine cable with hdmi then use specially designed ethernet jack with keystone wall plate.
Always use lightning protector
You never know how weather work and always make preparation by using lightning protector when you put cable cat 6 for outdoor. (mostly for POE use).
Never forget Cable Tester
Never assume that every new stuff is error free. I ever bought cable that make me think that my server configuration is wrong. 3 hours wasted only to realize broken cable. My friend check it using cable tester and save my day.
Use proper Cable
Don’t forget how to make cross over cable or strike. Watch the videos :
How to make ethernet cross over cable
Last one is always stock RJ45 and avoid cheap stuff. Bonus : brand never let me down. Trust it and you’ll be fine 🙂