A common failing
It is easy for us to forget about the Hereafter, as Allah (swt) says:
In the above verse Allah (swt) is speaking of the average Muslim.كَلَّا بَلْ تُحِبُّونَ الْعَاجِلَةَ (20) وَتَذَرُونَ الْآَخِرَةَIndeed you (all) love the fleeting present, while you neglect the Hereafter! [Holy Quran, 75:20,21]
How to be better than the average
The best believers are those who remember Allah often, and who always think about the Hereafter when they are reminded of Allah.
The Islamic wisdom behind remembering Jannah and Jahnnam often
Remember Paradise often so that it may feel closer. It is hard to be motivated to fulfill your Islamic duties if Paradise feels distant to you. The Quran describes this place to us hundreds of times in the Quran, because Allah knows that this is how humans are motivated to work toward it.
As a Muslim you recite Suratul Fatiha 17 times a day, or more. Verse four of this surah mentions the Day of Judgment. While reciting this verse you have a good opportunity to think about the Hereafter, so use it.