So you are in the situation that you want to sponsor your foreign spouse for permanent residency of Canada and don't know where to start. Here are some tips:
Married, common law or conjugal partners
First you need to pick an application class. There are three of them: married, common-law and conjugal. For all of them, you need to prove the genuineity of your relationship. For common-law, you need to prove that you have lived together for 12 months or longer. For conjugal, you need to prove that you have combined your affairs as much as possible but there are real immigration barriers or other barriers preventing you from living together or getting married. Conjugal is the hardest to prove. For example, if your partner could get a visit visa to come to Canada for 6 months and then apply for an extension to get the full year, even though they will not be allowed to work, that is not considered an immigration barrier. An immigration barrier is if your partner tries to get a visit visa to come to Canada and is repeatedly refused. Some people have had luck with the conjugal class but try to avoid it if possible.
Outland or inland?
Now you need to decide if to apply outland or inland. If your spouse is not in Canada and can not get a visa to go to Canada, you must apply outland. That means that you will send your application to Mississauga and they will approve you as a sponsor. The time that takes is usually 1-2 months to but current processing times can be seen here: http://www.cic.gc.ca/english/information/times/canada/process-in.asp#sponsorship After that, the application is forwarded to your local visa office. If your spouse is residing in a country other than the country of their nationality, you can pick which of the two visa offices you want. Otherwise it will be processed in their country of nationality. You can see the processing times here: http://www.cic.gc.ca/english/information/times/international/05-fc-spouses.asp
If your spouse is staying in Canada as a visitor or on some other visa, you can pick whether you want to apply outland or inland. Outland is generally faster and has appeal rights but a downside to outland is that if an interview is required, your spouse will have to travel to the visa office in the country where it's being processed. Inland has the downside that it's generally not advised that your spouse travels while you are waiting for your processing because it is a requirement of inland that they reside in Canada and if they are denied entry at the border for some reason, your application is gone. If an interview is required for inland, you may also have to wait a long time for it. The inland application would be sent to Vegreville and if all goes well, you would get a first stage approval, usually in 6 to 8 months. The current processing times can be seen here: http://www.cic.gc.ca/english/information/times/canada/process-in.asp#perm_res Then the file is forwarded to your local CIC office where you live and they will contact you for a landing appointment. Getting the PR with inland usually takes 12-18 months. If an interview is required for inland, Vegreville will not give first stage approval but instead will forward the application to the local CIC office without it and you will have to wait for them to have time for your interview. In some cases that can take a year or two. If you do get the first stage approval, your spouse will usually be eligible for health care and an open work permit. It is actually a good idea when applying inland to send an application form for a visit visa extension as well as the open work permit to be given at first stage approval all in one package so it's tied together.
Which method to pick depends on your situation. If your spouses country of nationality has a long processing time or your spouse does not want to have to travel there for a possible interview, then inland is the way to go. For faster processing and freedom of travel during the processing time, outland would be better. You can find the application forms for inland at http://www.cic.gc.ca/english/information/applications/spouse.asp and the application forms for outland at http://www.cic.gc.ca/english/information/applications/fc.asp
Avoiding potential problems with your application
The most common reason for people to be called for an interview is that the visa officer has doubts about the relationship being genuine. It is up to you to send immigration some quality data, emails, chat logs, phone records, photos, letters and other material to prove to them that your relationship is the real thing. Other reasons you might have problems with is eligibility of the sponsor. The sponsor can not be on social assistance, can not be bankrupt and can not have a record of violent crimes or crimes against family members. If that is the case, better talk to a lawyer and get that cleared up before attempting to apply.
Dependent children
If your spouse has dependent children, they must be included in the PR application, even if they are not coming to Canada. They will need to have medicals as well to keep the option open to sponsor them later. The only way that immigration will accept the application without those medicals is if the children are no longer minors and refuse to have it or if the children are in the full custody of their other parent who refuses to make them available for medicals. In that case, your spouse needs to sign a statement stating that they know that they will never be able to sponsor these children to Canada in the future.
Dependent children are classified as single and either under 22 years of age or if they are older, they must have been full time students since before age 22 or dependent on their parent due to a disability or medical problem.
Refusals due to income and medicals
You will be asked to provide information about your income but you will not be denied to sponsor your spouse and dependent children because you do not make enough money. It is possible though that if you make absolutely no money at all that immigration may ask you how you plan to support yourselves.
Spouses and dependent children are also exempt from the clause about excessive demand on health care so you do not have to worry about them being refused for that reason.
Sponsoring your spouse while living in another country
If you are a Canadian citizen, you can sponsor your spouse without being in Canada but you do then have to prove that you are planning on moving to Canada when your spouse gets approved for permanent residency. Such proof can include having arranged jobs, being accepted to college, having arranged housing or letters from friends & relatives stating that they know of your plans and that you can stay with them while you look for housing etc.
If you are a PR, you must reside in Canada in order to sponsor your spouse. You can chance short vacations (remember that a Canadian vacation is generally no longer than 2 weeks) but if immigration finds out that you are not in Canada, you risk getting your application refused.
Quote from LEON
), make sure to include letters from friends and family vouching for the validity of the relationship and also joint bills, rental lease, anything that you have. 
