tips to apply for TN visa

Hi,
I have all the requirements (VSC, job offer letter, Canada passport) at hands and will apply for TN at Vancouver, BC and WA's border. Has anyone had the similiar experience of applying over there ? I'd like to know such as what kind of questions do they ask? How long will it take? I assumed it's better to apply earlier before I fly to CA. Are there other things I should prepare or watch out? Thanks.