Dear Santosh Kushwaha,
You can select the trainer on the following competencies:
a) Job knowledge
b) Presentation skills (eye contact, whether the person has stage fear, ability to explain in sequence)
c) Communication skills (command over language, vocabulary, ability to give examples etc)
d) Ability to use the tools of presentation
e) Right personality (height, voice whether captivating etc)
f) Does the person has learning attitude
Thanks,
Dinesh Divekar