I consider myself a self-taught, sympathetic, and hard-working person. I consider myself a self-taught, sympathetic, and hard-working person.

Ordinarily you wouldn't leave off the "and" (this is called "asyndeton").

I consider myself to be a self-taught, sympathetic, and hard-working person. I consider myself to be a self-taught, sympathetic and hard-working person.

I consider myself a self-taught, sympathetic[kind?], hard-working person. I consider myself a self-taught, [kind?], hard-working person.

“Sympathetic” is grammatical but if you meant “simpatico” in the sense of “amable” “kind” is much better.

OIn my free time, I enjoy playing video games. In my free time, I enjoy playing video games.

OIn my free time I enjoy playing video games. In my free time I enjoy playing video games.

OnDuring my free time I enjoy playing video games. During my free time I enjoy playing video games.

OIn my free time I enjoy playing video games. In my free time I enjoy playing video games.

OIn my free time I enjoy playing video games. In my free time I enjoy playing video games.

Among my favorite ones are "Pro Evolution Soccer" and "Super Mario Double Dash". Among my favorites are "Pro Evolution Soccer" and "Super Mario Double Dash".

Among my favorite ongames are Pro Evolution Soccer and Super Mario Double Dash. Among my favorite games are Pro Evolution Soccer and Super Mario Double Dash.

In general, it's better to avoid using "ones" etc. and opt for something more specific.

Among my favorite ones are Pro Evolution Soccer and Super Mario Double Dash. Among my favorites are Pro Evolution Soccer and Super Mario Double Dash.

Great use of different sentence structure here.

In fact, the Internet has provided me with a lot of resources with which to do so. In fact, the Internet has provided me with a lot of resources with which to do so.

In fact, the Internet has provided me with a lot of resources to do so.learn a new language In fact, the Internet has provided me with a lot of resources to learn a new language

This is a better more formal way to write this.

In fact, the Internet has provided me with a lot of resources to do sofor that. In fact, the Internet has provided me with a lot of resources for that.

I will be writing stuff describing myself in writing more often. I will be describing myself in writing more often.

I suggest avoiding the word "stuff"; it's predominately used by children who don't know more precise words.

I will be writing stuffinformation describing myself more often. I will be writing information describing myself more often.

Stuff is very colloquial and ok when you are speaking