I woulld add that word order (especially in speach) is affected by a kind of rythm. The number of unstressed syllables between two stressed ones. In the sentence я буду тебя ждать there are usually two stressed syllables: 'буду and ждать. And you need less effort to pronounce the two stressed syllables between three unstressed ones than, for example, in word order like я буду ждать тебя, where there's only one unstressed syllable between the two stressed. (Although, of course, you can say that sentence with one stress on ждать.)