The rule about prepositions at the end of a sentence is a prescriptivist bugaboo from Classical Latin. Most grammarians agree it should not be applied to English.
It is a hypercorrection, like pronouncing the "t" on "often."
Do not end a sentence with a preposition when it can be avoided. Of course, there are always exceptions such as, "Where are you from?" and a few other examples. However, there usually ways to write/speak without ending a sentence with a preposition.
R1's solution illustrates the good practical advice offered by "The Elements Of Style" for dealing with issues of grammar: recast the sentence.
As Churchill allegedly once wrote when his editor 'corrected' a postpositional preposition "This is the sort of English up with which I will not put."
With regard to the OP's question, you could nitpick on a slight difference in meaning
a) Help (out) my friend = Assist my friend
b) Help my friend out = Get my friend out (of the house, a predicament, container etc)