How do you determine which keywords are easy to rank?

Say I've got a list of keywords, how will I find out the ones which are easy to rank?

How many monthly searches should I aim for as well (Using the google keyword tool),as a minimum

I'm planning to do clickbank offers marketed via youtube videos

Thanks!

My general guidelines:

Minimum monthly exact match searches: 500
PR of competition: Below 4

But of course this changes depending on how interested I am in the niche

Windip said:

My general guidelines:

Minimum monthly exact match searches: 500
PR of competition: Below 4

But of course this changes depending on how interested I am in the niche

Click to expand...

What's the best way of finding the PR of the competition? (Sorry I'm new to this). Is Market Samurai still useful?