The 29-year-old penned an 18-month deal with the Premier League's bottom side on transfer deadline day, leaving Tottenham to join up with former manager Harry Redknapp.
Jenas made his QPR debut less than 48 hours later, coming off the bench in Saturday's 0-0 draw with Norwich - his first competitive appearance in more than two months.
The former England international is now eyeing a starting berth but appreciates extra work is needed to get into shape.
"I was delighted to get out there for half an hour," Jenas told the club's official website.
"I felt composed and felt I kept the ball well. Now I will build from there.
"It was my first game since November, so it's been a while. But I'll be doing extra work in training throughout this week and trying to get myself to that level where the manager feels I am in a position to start.
"I know what my body needs, and if it needs more to get my fitness levels up, then I'll do more."