I am a high school student, my teacher told me that she wasn't a good student in her old times,but because she prayed tahajud,her results were magnificent.4 years back, at 3 30 am sharp I would wake up,almost every single day of the year,but now,i would just wake up on a usual daily basis,(6 am) ,what have I gone wrong? I see people that don't even pray have success in their life,but I don't want to be that way,what advice could you give,for me to wake up and pray tahajud?
The most important advice I can give you is to sincerely ask God for His help in performing tahajjud.
If over the years your closeness to God has decreased, then you must work on this. Many of the great early Muslims have said that sins cause God to forbid us from doing extra acts of worship, since these acts of worship are an honor that He grants.
Beyond that, your sleep schedule matters. If you try to get up at the wrong time in your sleep cycle, it can be very difficult to get up. Each person’s sleep cycle is different. If getting up four hours after you fall asleep is very difficult, you can try getting up four and a half hours or five hours after you fall asleep, or three and a half hours.
If you are not getting enough sleep, then it can be very difficult to interrupt your sleep to get up to pray. Try to get eight hours of sleep, for example by getting up four hours after sleeping, praying for 30 minutes or however long, then sleeping another four hours. Another way is to nap 7-8 hours after waking up in the morning (in the midday) so that the amount of total sleep you get in 24 hours is close to 8 hours (perhaps 7.5 hours at night and 30 minutes in the afternoon).
And if none of this works, you can pray tahajjud before going to bed, which is what I do, since interrupting my sleep makes it extremely difficult for me to work the next day (I do programming work, which is mentally demanding).