Are these well written sentences?

1. When I am writing, my words need to construct a clear picture for my readers.

2. I will avoid using slang in my writing.

3. Using irrelavant words, is one error I need to change in my writing.

4. I need to use a dictionary while I am writing, so that I can look up unfamiliar words.

5. It's important that I study the meanings and spellings of words that are confusing to me.

8 answers

Only one of the three commas you used is needed. Do you know which one?

All else is fine.
4. I need to use a dictionary while I am writing, so that I can look up unfamiliar words.
No.

The comma in #1 is correct. The others are not.
Thank you! I just caught that when I was rewriting that sentence.
I am still confused about the comma here. I thought you use a comma before for, and, or, so, but, nor, and yet?

4. I need to use a dictionary while I am writing, so that I can look up unfamiliar words.
... but not before "so that" -- when the conjunction is one of the FANBOYS, then the clauses are both independent, and a comma and COORDINATING conjunction is needed.

However, "so that" is a SUBORDINATING conjunction -- a very different thing.
http://grammar.ccc.commnet.edu/grammar/conjunctions.htm#subordinating_conjunctions
Okay, I get it now. Thank you for your help.
Oh, good! You're very welcome.