The most important point is that you change your desire and what is in your heart.
The goal is abstaining sins, it doesn't matter with a promise or without. The promise is something to motivate us.
Sometimes we try to abstain a sin and even we sincerely promise to Allah that we will never do it again but at the moment of deciding, we are weak and we can't keep our promise. after repeating this experience we may fear of committing the sin again and breaking the promise again and we try not to make any further promise because that would be a double sin.
In my opinion preventing from making this promise with Allah, what ever its reason would be, is ruse of devil, a step backward and getting farther away from Allah.
وَ لا تَیْأَسُوا مِنْ رَوْحِ اللّهِ إِنَّهُ لا یَیْأَسُ مِنْ رَوْحِ اللّهِ إِلاَّ الْقَوْمُ الْکافِرُونَ - (یوسف/87)
Indeed, no one despairs of relief from Allah except the disbelieving people
As long as we try to abstain a sin and we are not successful the sign of success is the sincerity in our heart. That is how Tawba should be: نَصوحا
يَا أَيُّهَا الَّذِينَ آمَنُوا تُوبُوا إِلَى اللَّـهِ تَوْبَةً نَّصُوحًا عَسَىٰ رَبُّكُمْ أَن يُكَفِّرَ عَنكُمْ سَيِّئَاتِكُمْ - (تحریم/8)
O you who have believed, repent to Allah with sincere repentance. Perhaps your Lord will remove from you your misdeeds
We should avoid even the situations that there is possibility to commit sin.