Could someone explain me more about the use of (in, at and on) and (for) and (to)?
In these cases:
1) It just will be a little step (on) or (in) a long road of the life and full of lessons learned.
2) I hope we preserve our friendship for or (to) the rest of our life.
3) Thanks to or (for) our relatives who are here today.
4) Thanks for being a support for all of us.
5) She will live forever in our memories.
6) We will put (on) or (in) practice for being the best every day.
7) The bonds of friendship that we have made in class and in or (on) the halls of the high school.

I consider I have some mistakes in theses sentences. I'd really appreciate, If someone has the time to help me with this question...

Question

Could someone explain me more about the use of (in, at and on) and (for) and (to)?
In these cases:
1) It just will be a little step (on) or (in) a long road of the life and full of lessons learned.  
2) I hope we preserve our friendship for or (to) the rest of our life. 
3) Thanks to or (for) our relatives who are here today.
4) Thanks for being a support for all of us. 
5) She will live forever in our memories. 
6) We will put (on) or (in) practice for being the best every day.
7) The bonds of friendship that we have made in class and in or (on) the halls of the high school.

I consider I have some mistakes in theses sentences. I'd really appreciate, If someone has the time to help me with this question...

Answer

I may can help you with the things that I'm about 
At: is used before small places like "I'm at home " "he is studying at school "
In: is used before large places like " I will spend my weekend in Egypt "
On: when you put something over something 
For and to have many uses it need a lecture to get them all 
1) in
2)for 
3)to but you have to complete the sentence like Thanks to our relatives who are here today, we had a nice time 
4 and 5 is correct 
6) i can't get the meaning of the sentence you wrote 
7)in 
Good luck