The 23-year-old striker, who netted 16 times for Carlisle last term, joined the Hornets on a free transfer from Brunton Park last week and is out to impress boss Malky Mackay from the off.
He told the Times and Star: "The manager is very good, very thorough with everything he does. He has left us in no doubt as to what he expects from all the players.
"I'm a confident person and I always set out to get 20 goals every season I play. I'll be aiming to do that but I don't expect to walk straight into the team.
"I will work hard over pre-season and hopefully give him something to think about."