When meditating on the breath, ...
I think you're practicing mindfulness of breathing? maybe.
And you're getting distracted by sensations of eye opening or vibrating...
I also read your comments where you mentioned
'Occasionally I will see a small light, but then realise my eyes are starting to open. Is this a distraction or my own fault?
Seeing small lights etc are called Nimitta, (see this)
Nimitta is different practice if your doing mindfulness of breathing, so you need to ignore that and also nimitta takes practice to see lights constantly otherwise your eye will start vibrating or get opened if you do it forcefully (especially if you're beginner).
Now coming to your main question, How to deal with distractions while meditating.
I had this problem and I will answer in points,
If your feeling some sensation like itching then itch it before meditating.
Avoid using computer and smartphones, half hour earlier (minimum) because eye-strain also creates problem.
If you're beginner then try doing meditation in low-light and safe places with less distractions.
Now comes the main point,
- Do concentration meditation for at least 7min. (I do this in morning)
When I say concentration meditation it's not like focusing on breath then some thoughts will come and you notice them and let them go etc.
No, I mean complete concentration, of course at beginning there will some distraction but remember to be fully concentrate on breath.
I remember a user in different platfrom saying this, 15min concentration meditation is equivalent to 30min less concentrated meditation.
- Last point, when you breath in enjoy your breathing in and when you breath out enjoy your breathing out. :)
When you breath in be aware that you're breathing in and when you breath out be aware you're breathing out.
It'll be better if you focus on natural breathing it will increase your concentration and also mindfulness.
And maybe later meditating becomes your habit and you don't need to remember most of the points which I mentioned.
Hope this helps !