I would suggest you to look for kits if you want to get a good quality of RNA.

You can use various kits like Qiagen kits or RNeasy kit if u want total RNA

For small RNAs, you can use the miRNeasy Serum/Plasma kit.

Good Luck

The easiest way is to use ready-made kits for example RNeasy Mini Kit from Qiagen or MagMAX MagneticBeads Kits from Thermo, or other kits with MagneticBeads because with their help you can get better RNA Quality.

thanks Maksim Domnich , Junaid Furhan

any precautions during sample collection and processing ?

because plasma seems to have too much RNA degrading factors.

If you are going to do PCR, you shoudn't use Heparin tubes for blood sampling, only tubes with EDTA, because Heparin blocks PCR. Store on -70 C, and try to defrost the sample not to many time.

thank you very much Maksim Domnich