"te", within that kind of sentence, means that a person will "make a verb" to him/herself, therefore you need to use "te" (or me/nos/se/etc... depending on the person to whom you are talking). I mean, if you say "vas a ensuciar los zapatos" you are saying to someone that he/she will get him/her shoes dirty (general meaning without "te"), but if you add "te", the sentence will talk specifically about the shoes he/she is using at that moment, and not about any shoe he/she posses.

Ensuciarse is the reflexive form of ensuciar. Here are some examples. Él me va a ensuciar los zapatos (he will get my shoes dirty) He will not get his own shoes dirty, he will get MY shoes dirty, that is why I use "me". If I will get my own shoes dirty: Me voy a ensuciar los zapatos. I use "me" because I will get MY OWN shoes dirty. In your sentence, "you will get your own shoes dirty" Tú te vas a ensuciar los zapatos. If "he will get your shoes dirty" I would use the same "te" even though it is he who will get them dirty. Él te va a ensuciar los zapatos.