"We will try to do it."
Translation:Spróbujemy to zrobić.
Generally, such words sound better in that position, but as always if you want to stress it, you can put it at the end:
We will try to do this, and not that = Spróbujemy zrobić to, a nie tamto.
This is true in most cases, so it's good to remember this rule.
"spróbować" is more like simple "to try", and "postarać się" like "to put an effort". Here they both work well.
Yes. Here, the verb that acts on "it" is "zrobić". Which takes Accusative, and as it's some general 'it', it's "to".
If it was just "We will try it", it would be "Spróbujemy tego", as "spróbować" takes Genitive.