Breathe deeply means to keep breathing. For some reason people tense up and forget to breathe.
Just by remembering to take deep slow breaths you will quickly begin to relax. Compare..
Hold your breath, and when you need a breath make it a quick short breath... notice the tension increase.
Now try breathing long and slow... deep whatever is comfortable... just slow full breaths... notice how much more relaxing that is compared to tense breating? That's all you're looking for... remembering to take long relaxing breaths.
Imagine a relaxing scene, something beautiful, or a symbol, just something that says to you peace, inner peace. Want to be sure it's a nice scene? Just check what happened to your breathing if it suddenly stopped, got panicky and shallow pick another scene. Make it an easy one that you can recall each time in a matter of seconds. A plant or flower works well, as does remembering a sunset or sunrise, a scene you've enjoyed before. If your breathing stays nice and relaxed or becomes even more relaxed, perfect. It's yours, so use that.
Alex