When you notice that your thoughts are roaming astray, say to yourself “BE HERE NOW” . And try to gently bring your attention to what you are doing.
Take short breaks from a long lecture . In that break, oxygenate and walk around the room for a couple of minutes.
You tend to pay more attention to something that is different . So you can change the topic which you are studying .
Make sure you sit up straight to aid concentration rather than sprawled out positiijn.
You should clear away any distractions.
Avoid usage of mobile while studying which would lead to distractions.
You should always be flexible in your schedule. If you need an extra hour on a subject, continue with it. Increase your power in achieving your goals.