3 or 4 biological replicates are usually sufficient.
No technical replicates are needed.
Do not perform studies in different batches.
Choose only one appropriate purification method for all your samples.
Use a DNase treatment during RNA purification to avoid gDNA contamination.
Avoid the use of nucleic acid based carriers during RNA purification as they can inhibit reverse transcription and produce cDNA product.
A260/A 280 ratio between 1.8 and 2.1 indicates NO contaminants such as proteins, phenol, ethanol and salts.
A260/A230 ratio >2.0 indicates the absence of organic compounds.
For FFPE samples, use DV200 criteria. Do not use samples with a DV200 <30%, they are too degraded.
RNA Integrity Number between 7 and 10 indicates good quality.
Using a Nanodrop for initial estimation and a dye assay for a higher accuracy.