As Crawford has explained very clearly above! You must be sure you meet all the requirements, financial, accommodation and relationship and that you have evidence of each of these categories, with original documents as proof. You should make sure you have all your supporting documents in place ( the most recent financial ones have to be within 28 days of your application) because once you have given your biometrics, you have to submit your supporting documents quite quickly, I think. Not sure of the process when applying from Canada. Don't forget Appendix 2!