Start smaller than you think
The most common mistake with a trainer is starting too big. Choose a slim, smooth trainer made of body safe silicone and use a water-based lubricant. Short sessions of a few minutes are enough. Stay on one size until it feels easy for several sessions in a row, then move up one step. Wash the trainer with warm water and mild soap after every use and let it dry fully.
See trainer sets in our shop and read the deep throat trainer guide.