Lam of Allah: heavy after a preceding fathah or dammah; light after kasrah. Ordinary lam remains generally light. The opening form «اللَّهُمَّ» is read with heavy lam.
Vowelled ra: heavy with fathah/dammah, light with kasrah.
Still ra: heavy after fathah/dammah and usually light after an original kasrah; remember the exceptions of a temporary vowel, a previous word and a following emphatic letter in the same word.
Ra at a pause: assess a further-back vowel when needed, the case of still ya, special cases such as Misr/Qitr, imalah and rawm.
Rules reach their full purpose only through listening, guided practice and correction. The next lesson begins the rules for unvowelled and doubled mim.