Sa(shadaj) is the most important and prominent swar in indian classical music, from this all the other notes or swaras have emerged therefore it is very very and very important to practice SA as much as possible by any vocalist.
How to practice?:
Step 1: Choose your natural scale in which your voice can freely move in all the three octave.
In general the male range is between( C to D#) some of them can be lower or higher than the said range but im talking about 90% of the people who fall under this range.
step 2: Identify your exact pitch and play it on TANPURA(either electronic or accoustic).
Step 3: Match your voice with the pitch that you have selected without putting any extra effort or physical pressure( be as relaxed as possible and its the most important to be attentive to your voice production technique while singing) therefore sing in front of your guru for some days to avoid any mistakes.
Step 4: Sustain your voice in the pitch you have matched with(use stopwatch to see how long can you sustain in one breath) normally it should be 15 sec min in the beginning and should go up tp 60 secs at least.
Step 5: Dont thank me just try it for 3 weeks and see the differance in your voice.