Common mistakes for new Na'vi learners to avoid

[Tirea Aean]

May I propose an addition to OP:

Mistake #8: Adpositions.
mìhelku (in the house/home)

An adposition in Na'vi is it's OWN SEPARATE, NON-ATTACHED WORD. except when it is attached to the end of the noun. This is a choice. Adpositions are never attached to the beginning as a prefix. There is a space between the adposition and the noun when it comes before the noun.

The only things that may be attached to the end OR the beginning is -a- for attributive adjectives(still must be on correct side), and -pe+ for forming question words from nouns.

Correct: mì helku or kelkumì

['Oma Tirea]

...which reminds me, don't forget about lenition, and that mì+, as common as it is, causes lenition.  They say no one expects the lenition...

/reminder

['Oma Tirea]

Oh, and one more thing /doublepost:

Mistake #9: Pronunciation.

{to be described in extra-thorough detail}

[Neytete]

  oh wow am I confused!! I just need help in general....

[Blue Elf]

Can you specify in which area you need a help? Probably is good idea to create new thread here to describe and discuss it.
IMHO you should try to study some simple material to get some basics and learn basic vocabulary. I recommend these:
Le'eylans prezi lessons for Ngaynume (some basic vocabulary and rules)
Na'vi in a nutshell (simplified grammar)
Basic vocabulary a little outdated, some words change. but still useful
Learn Na'vi easy way workbook by KP

After you learn some basics, you should be able to ask more specifically