Never go up in minutes/miles by more than 10% per week.  This decreases your chance  for injuries.

When training for your swim, make sure you go a little farther then your needed distance.  You will definitely have confidence then.  Swimming can be scary - especially if one can't touch or see the ground.

Make sure to do a few 'brick' workouts several weeks before your first tri.  These will help you immensely for the bike to run (T2) transition

Do some open-water training if possible.  At least 1-2 times prior to racing.  Open water swimming will be more challenging.  Just make sure you have somebody looking out for you if you get into trouble.

Don't train hard the last two weeks before the race.  It's too late for improvement.