If you need to set a smaller hint for your edit text, you can set the hint this way:
myEditText.setHint(Html.fromHtml( "<small><small><small>" + getString(R.string.hint) + "</small></small></small>"));
Also, you can set the size in the string resource file where is the string for the hint.
<string name="edit_text_hint"><font size="15">My hint string</font></string>
and in the xml file just set the hint as usual:
android:hint="@string/edit_text_hint"