Lot of people ask lot of questions about Canadian immigrations.. but problem is.. people don't spend enough time reading proper guide.. a beautiful, well-explained guide. Which is so easily available on internet: http://www.cic.gc.ca/english/pdf/kits/guides/EG7.pdf  Everything is clearly outlined in this guide.

Then you download all the required forms from:
http://www.cic.gc.ca/english/information/applications/skilled.asp

Then, there is one more thing people need to be careful about - Visa-Office Specific Forms (this is where you can get info on what additional documents you are required to submit based on which visa-office you are applying to. This also tells you about getting Police Clearance Certificates - there is a "Web" link given in the document checklist. If you go to that website, they have exactly mentioned where to contact at each country from where you are required to obtain police clearance certificates.
http://www.cic.gc.ca/english/information/applications/skilled-mission.asp

Anyways, here is the link for Police Clearance Certificates:
http://www.cic.gc.ca/english/information/security/police-cert/index.asp

English Proficiency:
You don't have to have IELTS if you have studied in English medium and your work experience letter clearly mentions that your work environment were in English Medium. So if you have degree from USA... you don't need IELTS or TOEFL. But remember, if you have high scoring in IELTS in all four sections (reading, writing, speaking and listenening) as mentioned in the guide, then it's 100% certainty that you will get 4 + 4 + 4 + 4 = 16 point in Language Factor. Otherwise, it's at their discretion!!!! Thumb of rule is, if you have accumulated enough points in other Factors and only few points from Language Factor will be adequate to exceed the pass mark of 67 points comfortably.. then don't take IELTS.

GOOD LUCK !!