The experienced winger, who turns 33 next month, scored a hat-trick in their 36-18 Betfred Challenge Cup win at Leigh Centurions.
He links up with the national squad tomorrow and Watson – who got his first Giants win since switching from Salford Red Devils – said: “Jermaine’s been quality since I came in here.
“He’s one of those who’s willing to learn and wants to learn and get better. He’s great to work with.
“There’s certain things we noticed before (joining Giants) that we’ve been able to work with Jermaine on to make him better or to try and fix him up.
“That will be ongoing. It’s like we’ve said with the team; you don’t win anything in the first few weeks of the season.
“I do have belief that these players here individually are very, very good players.
“But what we have to do is get them to buy into the team ethic that we need consistently to be a top team.”
After defeats against Hull FC and Catalans Dragons, they showed that in patches yesterday especially when 18-0 ahead inside the opening half hour.
Watson admitted: “It was a lot better. It’s not the finished article by any stretch of the imagination.
“We’ve a lot of improvement to do in and amongst that. But it was better from us. It’s been building. The first 20 minutes were really, really good and we had that composure and field position early.
“Overall, it was another step in the right direction.”
Watson is hopeful captain Aidan Sezer could return from injury for his first game of the season when they visit Hull KR on Friday.
Leigh coach Jon Duffy is still awaiting his first success in either competition since being promoted.
“Our start was horrendous; it was not good enough,” he said
“I was happier with the second half. We clawed our way in.
“But you can’t have a single play off at this level. We started jogging for free balls and you just can’t do that.”
Betfred Challenge Cup quarter- finals: Hull FC v Wigan Warriors, Castleford Tigers v Salford Red Devils, Catalans Dragons v Warrington Wolves, St Helens v Huddersfield Giants Ties to be played on May 7/8 at neutral venues).
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