When I practice Anapana meditation,I often get a feel that I tried to alter my breathing instead of observing natural breathing.So,how can I observe natural breath?What are the best tips for this?
A simple and natural way to relinquish breath obsessions is to count your breaths. This is a traditional Zen meditation practice that I still use 4 decades after I learned it. It works because it gives your grasping mind something to do. It's actually quite difficult to maintain a count. One has to relinquish distractions in order to not lose count. And that is actually why breath counting of any sort is initially effective.
With extended practice, the counting itself becomes a distraction since it engages the verbal processes. In the meditation practice guide of MN44, we have:
MN44:17.2: “Verbal processes cease first, then physical, then mental.”
So to deepen the practice, we have to relinquish the numbers. One way to do so is to switch to something like prayer beads where the counting is relinquished while retaining the mindfulness of the passage of time. Or one can simply follow the breath in and out as recommended by the suttas.
Consult with a meditation teacher for individual advice on breathing.
Short answer: no need to worry about it.
Long answer... If you find yourself trying to control your breathing, then observe yourself trying to control your breathing. There is some discontentment there: maybe some thought process is worried that you're not breathing 'correctly,' or some part of you is bored and wants to play with the breath. But as you watch yourself trying to control your breathing your breathing will become natural, because you're no longer identifying with the part of you that's trying to control it. And as your breathing becomes natural, that part of you that's trying to control it will get stagnant and fade, and you'll fall back to watching your breathing.
Breathing is breathing. There's no right or wrong to it, and you can only have so much control over it in any case. And really, controlling your breathing is not 'wrong'; that is literally how you are breathing at that moment, so all you need to do is watch it as you'd watch any other breathe. Part of the practice here is quell the idea that anything needs to be done. No need to control the breath, no need to suppress controlling the breath: either way, breathing will merely continue.
Simply give up the intention to watch the breathing and only have the intention to sit with a quiet mind.
It is not necessary to bend or direct the mind to watch the breathing. If the mind is quiet, the mind will automatically know the breathing.
The Buddha did not teach to watch breathing. The Buddha taught to abandon craving.
The word "mindfulness" means to "remember" to apply the teachings (of abandoning craving). "Mindfulness" does not mean to "observe".
"Anapanasati" means "mindfulness with breathing". It does not mean "mindfulness of breathing".