A list of guides that I find useful (last update : 25/11/17)

Begginer guides of the game

The Smash dictionnary
Asmodean on Smashboard
Common Noob mistakes
Some rules I followed to get better, by LunInSpectra
SFAT guide on neutral

The four aspects of melee by Wobble
Breaking down safe on shield
A few basic tips every "new" competitve player should know.  

Meta

Stages
Stages analysis
Ledge trumping
Everything about autoshielding by Esam

DI :

    DI : Crazy hand post

    LSI : Twitter post
Movements in smash 4 Crazy hand post
Comprehensive guide to frame data
Get good, a guide to get better at neutral
At the start of the game, what are the things to look for    

Training advices

ADHD's guide on how he became good at Brawl.
Cpt faceroll on how he got better quickly
Theory of improving in fighting games

Llod's guide on improvement

Ledge trump

Mindset

MIOM : Establishing tournament consistency
Five Things to Think About If You Want to Do Well at Tournaments
Approaching smash with a growth mindset

The Burden of Winning and a Sustainable Mindset (Smashbl0g)

Tourney Etiquette – Handshakes, Hygiene, Coaching, and more (Smashbl0g)
Mental Manipulation: How to Prepare Your Mind to Smash
Struggling? Take a break! (Inspiration post)  
Keep calm during tournaments
Maxman33's post on improvement 
The mentality behind a player in training

Misc

MIOM :  The Curse of the Two-Person Meta

Melee library : Lots of melee guides.  Some of them (mindgame, training) can apply to smash 4

The Power of Knowing: Types of Information in Smash
Smashvods
Lag's effect on your gameplay ?
A way to "Quantify" your player skill
How would one go about finding a group of people (or person) to consistently play with? (Crazy hand thread) 
Leveling Up in Smash 4: Your Character and the Importance of Fundamentals

https://www.reddit.com/r/SSBPM/comments/2rked3/mind_over_meta_archive/