In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatuh
Istibra is a process that ensures that all of the droplets of urine are pressed from the urethra.
There are several practices that will assist a person in relieving himself of this problem.
1. One should urinate in the crouched sitting position and not while standing.
2. Once the urination has ended, the remaining drops in the urethra have to be forced out. This can be done by forcing yourself to cough whereby the movements of your body force out the remaining drops.
3. Another way is to place toilet paper on your private part and take several steps whereby the urine drops leak out onto the toilet paper. However, the best and the most tried and tested method is as follows:
After urinating from the sitting position, use the middle finger and / or index finger of your left hand and press upon the urethra starting from between the scrotum and the anus moving forward towards the penis forcing any urine drops. After repeating this process several times, wash the private part as you would normally do whilst making Istinja and thereafter make sure to dry the private part with toilet paper.
As an extra precautionary method, one can place a piece of toilet paper in his underpants to absorb any leftover droplets of urine. One should only commence performing Wudhu after feeling assured that no more drops of urine will come out. Before, performing Salaah the toilet paper should be removed or replaced with clean toilet paper.
By applying the above mentioned methods of Istibra, Insha Allah, your problem would be solved.