Usually works: Create style-rtl.css (textual blank file) in addition to existing style.css file, and use it to override default LTR and align left definitions.
For example, add the following, ,to the empty styel-rtl file:

html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, font, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead, tr, th, td {
    direction: rtl;
    text-align: right;
}

And for the menu, which is usually more tricky:

#main-menu ul {
  float:right;
}