Jules you just have to be consistent with your starts/endings. With treble crochet you do a ch3 starting train which counts as a stitch, therefore you skip the first stitch. You then have to make sure that at the end your last treble crochet goes into the ch3 on the row below. Does that make sense.
BUT with DC (UK) you don't do that, it's just a single chain at the start, doesn't count as a stitch so you crochet into the first stitch (or loop of foundation chain), and you don't crochet into the chain at the end because it doesn't count as a stitch.