We consider grammar based text compression with longest first substitution, where non-overlapping occurrences of a longest repeating substring of the input text are replaced by a new non-terminal symbol. We present a new text compression algorithm by simplifying the algorithm presented in [dl. We give a new formulation of the correctness proof introducing the sparse lazy sufix tree data structure. We also present another type of longest first substitution strategy that allows better compression. W e show results of preliminary experiments comparing grammar sizes of the two versions of the longest first strategy and the most frequent strategy.