First attempt at a sentence.

[Eywa'ite]

Okay, so I decided to try and translate one of my favorite quotes into Na'vi.  The quote is: "Your vision will become clear only when you look into your heart."  What I came up with was:

Äie nga-yä l<ay>u law nì'aw pehrr nga-l kame txe'lan-it nga-yä.
Vision you-GEN be-FUT clear only when you-ERG see/understand heart-ACC you-GEN.

But I'm pretty sure I screwed up somewhere.

[Carborundum]

The only problem I can see is your usage of pehrr. Pe+ is a question marker, so you can use it in sentences like "when did it happen?", but not "it happened when we hunted". For the second, you want tsakrr, that-time.
Other than that, it looks good. Well done for a first sentence.

[Eywa'ite]

Oh, that makes sense.  Irayo!

[Kì'eyawn]

Kaltxì, ma Eywa'ite.  I agree with Carborundum's suggestion, but then i would also add that i think the word äie means "vision" in the sense of, for example, "I had a vision of Eywa."  So, if that's the meaning you were going for, then great.  If not, your options are tìtse'a (from tse'a, "to see," in the physical sense) or tìkame (from kame, "to See," in the spiritual sense).  And then i would change lu to slu, which is the Na'vi verb for "become."  The last thing i would point out is that the genitive form of nga is actually ngeyä.  So, adding Carborundum's suggestion and assuming you wanted to keep äie, your sentence would be

Äie ngeyä slayu law nì'aw tsakrr a ngal kame txe'lanit ngeyä.
(Lit. "Your vision will become clear only at the time that you See your heart")

Eywa ngahu, ma tsmuke.

[Eywa'ite]

Kaltxì, ma Eywa'ite.  I agree with Carborundum's suggestion, but then i would also add that i think the word äie means "vision" in the sense of, for example, "I had a vision of Eywa."  So, if that's the meaning you were going for, then great.  If not, your options are tìtse'a (from tse'a, "to see," in the physical sense) or tìkame (from kame, "to See," in the spiritual sense).  And then i would change lu to slu, which is the Na'vi verb for "become."  The last thing i would point out is that the genitive form of nga is actually ngeyä.  So, adding Carborundum's suggestion and assuming you wanted to keep äie, your sentence would be

Äie ngeyä slayu law nì'aw tsakrr a ngal kame txe'lanit ngeyä.
(Lit. "Your vision will become clear only at the time that you See your heart")

Eywa ngahu, ma tsmuke.

That was so helpful!!  Irayo!  One question though: What is the "a" in between tsakrr and ngal for?

[omängum fra'uti]

The "a" is attributive, it's basically turning "ngal kame txe'lanìt ngeyä" into an adjective phrase describing "tsakrr".

Though I'd write it SLIGHTLY differently...  No need to use tsakrr, "krr a" works fine for "when".  I'd also use the perfective for kame (kolame) and use "mì te'lan" rather than "txe'lanit" (See in your heart vs see your heart) - closer to the original and from what we've seen possibly a metaphor the Na'vi would use).

So...

Äie ngeyä slayu law nì'aw krr a nga mì te'lan ngeyä kolame
vision 2-GEN become-FUT clear only time ATTR 2 in heart 2-GEN see-PFV
Your vision will become clear when you see in your heart.

You could also use tìng nari instead of kame to be even closer to the original in translation, but kame may produce closer to the meaning of the original.

Äie ngeyä slayu law nì'aw krr a nga mì te'lan ngeyä tolìng nari
vision 2-GEN become-FUT clear only time ATTR 2 in heart 2-GEN give-PFV eye
Your vision will become clear when you look in your heart.

[Eywa'ite]

The "a" is attributive, it's basically turning "ngal kame txe'lanìt ngeyä" into an adjective phrase describing "tsakrr".

Though I'd write it SLIGHTLY differently...  No need to use tsakrr, "krr a" works fine for "when".  I'd also use the perfective for kame (kolame) and use "mì te'lan" rather than "txe'lanit" (See in your heart vs see your heart) - closer to the original and from what we've seen possibly a metaphor the Na'vi would use).

So...

Äie ngeyä slayu law nì'aw krr a nga mì te'lan ngeyä kolame
vision 2-GEN become-FUT clear only time ATTR 2 in heart 2-GEN see-PFV
Your vision will become clear when you see in your heart.

You could also use tìng nari instead of kame to be even closer to the original in translation, but kame may produce closer to the meaning of the original.

Äie ngeyä slayu law nì'aw krr a nga mì te'lan ngeyä tolìng nari
vision 2-GEN become-FUT clear only time ATTR 2 in heart 2-GEN give-PFV eye
Your vision will become clear when you look in your heart.

Irayo!  That was very helpful