Make sure that you are a confident downhill skier. You want to be a strong intermediate on piste: meaning you are completely comfortable on blue and red runs, and pretty solid on black runs and nearby off-piste.
For your first tour, make sure that you keep it simple by choosing a gentle route. It will help introduce you to your equipment and start to establish the basic technique.
However, the most important piece of advice before you embark on your first tour, is to not go out alone. Whilst the backcountry offers so many incredible opportunities for exploration, it can also be dangerous. Ideally, take your first trip with a guide or friend who is experienced in ski touring. They will be able to not only teach you crucial technique, but also offer important safety advice, and tips on what to look out for.
If possible, it is also really beneficial to undertake some backcountry safety training before your first trip, learning basic mountain safety along with how to properly check the weather and avalanche hazard levels. You will also need make sure that you are familiar with how to use your transceiver, probe and shovel in the case of an avalanche. Some basic training with this equipment is invaluable.