The easiest way from Kitsilano to downtown Vancouver is the bus. Route 2 runs between Kitsilano and Burrard Station on Cornwall and MacDonald, and Route 4 runs along 4th Avenue and into the downtown core.
Buses from Kitsilano into the core
Route 2 starts in Kitsilano, follows Cornwall Street and MacDonald Street, and ends at Burrard Station on the Expo Line. From there you are in the middle of downtown or can ride one stop to Waterfront. Route 4 connects UBC with Powell Street in East Vancouver through downtown, and it runs along 4th Avenue and stops near Granville Island. Route 44 links UBC and Waterfront Station along Burrard Street, which helps if you start near Burrard.
Which one suits you depends on your block, so type your address into the TransLink trip planner and it will show the nearest stop and the next departure. Pay with a Compass Card or Compass Ticket, and the fare covers a transfer within 90 minutes on bus, SkyTrain and SeaBus. Current fares are on the TransLink website.
Riding the Seaside Greenway
Cyclists can follow the Seaside Greenway, a waterfront path that runs through Kitsilano and False Creek toward the Convention Centre. It has separate sections for walkers and riders, so stay in the cycling lane. The path runs on past Yaletown and the Olympic Village, so you can pick whichever area you want to reach. Mobi bike share has stations around the city, and you can find prices on the Mobi site.
A cab or rideshare for the trip
Kitsilano is a short drive from downtown, and a cab is useful if the weather is poor, if you are carrying bags or if you are leaving late. The taxi fare estimator gives a rough figure for the trip, and Uber calculator lets you compare it with a rideshare. Vancouver taxi covers pickups in the city.
Traffic on the bridges is heaviest at the morning and late afternoon peaks, so a car trip can take noticeably longer then. If you are heading downtown for an event, give yourself extra time for road closures, and check the venue page for transit notes.
Parking downtown is metered or in paid lots, and rates change by location and time of day. Look at the signs and the City of Vancouver parking pages for current prices before you leave the car.