Plasmid: 

Single, bright bands, high purity (no protein, RNA, or other impurities), total amount approximately 1-2 μg.

Bacterial culture:

Preferably fresh bacterial culture without glycerol, avoiding contamination. Ensure the culture period is not too long to prevent bacterial aging and potential failure in plasmid extraction.

Plate:

Fresh bacterial colonies available, not older than 3 days, with identifiable single colonies for picking.