Prices: make sure your prices are competitive in Competitors’ bids section, taking into account your campaign settings.
Categories of the sites: the fewer of them you select, the longer it takes to start your impressions.
Browsers: desktop only? Desktop traffic is only about 20% in our system, so the competition is higher.
You have chosen the targeting with little traffic. You can check out the traffic volumes and average prices here.
Your clickunder rate differs by more than 20% from the TOP targeting rate. If the advertiser sets the rate 20% higher than the nearest competitor, he gets the advantage of buying in all the traffic on the selected targeting.