Extremely impressive. You're right that pronunciation is key, if you'd had better teachers, you could've saved a lot of time, but in any event, you can perfect your pronunciation with continued "study"!

You actually write better English than a lot of native speakers. I've corrections in ALL CAPS because I'm too busy to fool around with all those fancy colors and stuff. Normally, all-caps should be avoided.

Hello guys!
English is one of the most interesting foreign languages for me to learn. However, teachers from my secondary and high schools focused way too much on grammar and writing skill. Actually, their pronunciation WAS wrong :( This RESULTED IN students' speaking and listening skills BEING pretty terrible. Things BEcame better when I attended university. During those 4 years, I met lecturers and friends WHO SPOKE ENGLISH more correctly. But to be honest, there's still a bunch of mistakes WITH my pronunciation and INtonation. That's why I try my best to find ways to improve my speaking skill. LUCKILY, I had a chance to come to Phuket, Thailand. Many native English speakers, as well as non-native, come here as tourists. Thus I can talk to them face to face. That's great!

You should spell out numbers like "four" (4).
The phrase "pretty terrible" sounds native, just be aware it's rather informal.
"there's still a bunch of mistakes" is perfectly natural spoken English, just be aware the "correct" form is plural: "there ARE still a bunch of mistakes."
"Thus" is much more formal than the rest of your writing, so it might be more natural to use "so" or "which means." Also, I wouldn't use a period (full-stop) after "tourists" -- I'd just use a comma, or maybe a dash or semi-colon.

Welcome to italki.

I have just discovered italkicom and I am already in love with it. It's time to start practicing my writing!

Hello guys!

English is a really interesting foreign language that I would like to learn (There are a lot of ways you could re write this sentence, you have a lot of options :))

However, my secondary and high school teachers focused too much on grammar and writing skill. Their pronunciation was wrong/incorrect. The students' speaking and listening skills were pretty terrible because of this. 

Things became better when I attended university. During those four years, I met lecturers and made friends with people who had better english speaking capability. Even so, I still make a lot of mistakes with pronunciation and intonation. 

That is why I always try to find ways to improve my english speaking skill/skills. I'm glad I had a chance to come to Phuket, Thailand. There are many native english speaking tourists as well as non native tourists that I am able to talk to face to face. It's great!

Just found italki.com and already in love with it. Time for practising writing!!!('Time to practice writing' or 'Time for writing practice')

Hello guys!
English is one of the most interesting foreign languages for me to learn. However, teachers from my secondary and high schools focused way too much on grammar and writing skill. Actually, their pronunciation were(was wrong) wrong :( This caused the fact that students' speaking and listening skills were pretty terrible(So this caused the students to have poor speaking and listening skills.). Things came better when I attended university.('Things got better' or 'things were better')During those 4 years, I met lecturers and friends with more correctly English speaking('with more correct english'). But to be honest, there's still a bunch of mistakes of my pronunciation and tonation('mistakes with my pronunciation an intonation'). That's why I try my best to find ways to improve my speaking skill. Gladly I had a chance to come to Phuket, Thailand. Many native English speakers, as well as non-native, come here as tourists('many native and non-native English speakers'). Thus I can talk to them face to face(So I can). That's great!