I think they are the dirtiest after raining.
When the dirt gets wet, also my shoes get wet, and the dirt stick to my shoes...
And also, now we are preparing for the sports day, and we practice at the play ground.
So the sand makes my shoes dirty.
Those are the situations that makes my shoes the dirtiest.

Love one another - John 15:12

= 
I think they are the dirtiest after raining.
When the dirt gets wet, my shoes also get wet, and the dirt sticks to my shoes...
And also, now we are preparing for the sports day, and we practice at the playground.
So the sand makes my shoes dirty.
Those are the situations that make my shoes the dirtiest.

= "also" can be put before the noun phrase or at the beginning with a comma (,)
example: also, my shoes get wet
= dirt is also considered singular, therefore requires a singular verb 
= "situations" are plural, thus, it needs a plural verb
= Overall, the sentences were great!