I play relatively flat and hit good passes. Here is what I hate so maybe it will work for you.
- Higher balls. I find with my flat stroke that the perfect spot for me to hit the ball is relatively low, I struggle to hit a good pass up higher, especially on the backhand side (I have a 1HBH). A lot of players hit hard, low approaches, I just love to pass off those
- Angles. When I hit, I find that because I don't use a lot of spin, I have to take power out of the ball a lot to hit an angle. This means two things for you, firstly I tend to pass a lot down the line, so when you run in, try and close this off. Secondly its harder to hit a flat shot off a ball when I'm running, so I tend to slice these. If you get me moving from side to side before you hit the approach, its a much harder shot for me to make.
- Don't get too close to the net. With the passing shots going mostly down the line and the lobs thrown in, stay back a bit further from the net than usual. It will make your volleys a bit tougher but you're more likely to get the lob (either for a smash or running) and if you close the angle on the down the line shot better you'll probably still make the volley comfortably (remember its hard to go for a short angle cross court).
Edit: Its hardest to hit a pass from the middle of the court so if you are approaching and you haven't run me off the court on the other side, hit it down the middle
Just my ideas, some may work for you some not, but I know thats what I find difficult.
Two things I love are people that hit very hard (I can just take out the power and use their's to hit it flat back) and people that like to hit very loopy strokes as my balls tend to fly lower and it makes it harder for them to hit in their zone.
Hope it helps