In general Taxi in Russia is of the same price as public transport in many European countries, hence it is advised to use Taxi.
Recommended way to use Taxi is via mobile applications. Of course, there are lots of different companies that provide this service. We recommend you the following.
Gett mobile application. Install it via Google Play or go to the Gett website and provide your phone number to get a download link. If you want you can install the app in advance. It will be possible to use this app with the new local sim card with unlimited mobile internet later.
Please, attach your bank card as a payment method. This way you won't need to pass any money to Taxi's driver and may use the service once you have landed at Saint-Petersburg:
You may use the following promo code ("Coupon code" in the 2nd image above): GTJWVFP
RuTaxi is another convenient application. The procedure is the same as with the Gett. Make sure to set "I do not speak Russian" checkbox if you need.
As any major city in the world Saint-Petersburg has a wide range of public transportation: Metro, Trams, Buses etc. You will need a rechargeable e-ticket for public transport: link
Here is how you can get from the airport to the conference hotel using public transport: link
Probably, you may want to install Yandex.Transport mobile application if you plan to use public transport. With this app it is possible to choose the best routes, track public transport in real time, find your stop on the map, keep tabs on traffic jams, etc