YO DUDE its been awhile

Hajimemashite!

I saw your sign, so I got extremely tempted to fix it... in the interest of spreading the Japanese language!

Anyways... the -masu form is used exclusively on the end of the sentence, so after 'wakarimasu' you need a full stop. Also, 'soshite' is usually used on the beginning of a sentence, so it fits nicely.
Next, instead of 'hanashimasu' (I speak), you probably wanted to say 'hanasemasu' (I can speak). Once more, a full stop should come after -masu.
When speaking, after 'Demo' you'd pause for moment, so put a comma there. 'jozu' would usually be transliterated as 'jouzu' or 'jōzu', as the 'o' sound is elongated.
'jarimasen' should be 'ja arimasen', or a more polite form 'de wa arimasen' ('ja' is informal for 'de wa').
Lastly, 'so' also has the elongated 'o' sound, same as the above-mentioned 'jouzu', and is usually transliterated to 'sou' or 'sō'.

So in the end, it would go something like this:
Ore wa nihongo ga sukoshi wakarimasu. Soshite, hanasemasu. Demo, mada jōzu de wa arimasen.
Or in Japanese writing system:
俺は日本語が少しわかります。そして、話せます。でも、まだ上手ではありません。

I hope I've been of some help, and that you'll continue to improve your Japanese ^^
And yeah, I'm quite impressed with it, since it seems you didn't study it formally. I couldn't even make a proper sentence before coming to Japan >.<

Sayounara!

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"Whenever you find yourself on the side of the majority, it's time to pause and reflect." -- Mark Twain

"We are but packets in the Internet of life" -- Mike, UserFriendly.org

Check my sister's works.

Thank You!!

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wait for it....wait for it.....