The classical Buddhist tradition has a name for the things that get in the way: the hindrances. They are not exotic. Everyone meets all of them. Knowing their names helps, because it lets you say, oh — that's restlessness, not 'I am uniquely bad at this.'
Drowsiness
You sit, you close your eyes, and within two minutes you are nearly asleep. This is common, especially in the evening or after a meal. Try: opening your eyes halfway, lowering the gaze to the floor. Sitting up taller. Taking three slow, deeper breaths. Splashing cold water on your face before you sit. Sitting earlier in the day. If you are deeply tired, sometimes the answer is honest — your body needs sleep, not meditation, today.
Restlessness
Your knee itches, your mind races, you cannot stay still. Try: not scratching the first itch. See if it passes on its own. Most do. Try a shorter sit — three minutes instead of fifteen. Or try walking meditation: slow steps, attention on the feet, breath in time with the pace. Stillness will come. It does not have to come today.
Self-judgment
'I am terrible at this. Everyone else can do it. My mind is broken.' This is the most common hindrance and the most painful. Try: when you notice the judging voice, treat it as one more thought — note it gently, 'judging,' and return to the breath. The judgment is not the truth. It is just the mind's habit, loud today.
It can also help to remember: every teacher in this entire tradition, in every lineage, sat through this. None of them were good at it at first. Many of them were never serenely good at it. They just kept sitting.
Boredom
Nothing is happening. You are not having a beautiful experience. You are just sitting there, and frankly, you are bored. Good. Boredom is the mind realizing it has nothing new to feed itself. Stay. Underneath the boredom, if you do not run, is something quieter than boredom.
Strong emotion
Grief, anger, anxiety, a memory you did not invite. The breath has loosened it. Do not push it away. Do not get lost in the story of it either. Find a place in the body where you can feel it — chest, throat, belly — and breathe with the sensation, not the story. If it is too much, open your eyes, place a hand on your heart, and end the sit. Coming back tomorrow is fine.