Well if you don't have a wall - then I guess you don't have a gym either. So we are talking about some serious limitations.
One thing you could do which I found helpful for on court quickness is jumping rope. I am not still not a great rope jumper - but I swear to god I feel faster and quicker. You can buy a jump rope for few bucks. Then you can do a little workout like.. jump rope 50x - then do pullups.. jump rope 50x - then do body weight squats - jump rope 50 x then do body weight lunges..
Another thing you could do is run suicides..if you have space for that. Of course few people are self motivated enough to run suicides. There is a tennis style suicide you can do..
(From the tennis server - feet don't fail me now)..
http://www.tennisserver.com/turbo/turbo_99_12.html
You can run these sprints on tennis courts, in a gym or on a large field. If you are running on tennis courts, you want to run the equivalent of 2 1/2 court widths for each sprint. I usually begin at the center service line on one court and then run until I reach the far sideline of a court that is two courts away from the starting point (thus, 2 1/2 court widths). If I am running in a gym, I run the entire length of the basketball gymnasium for each sprint. If I am running on a field, I try to run approximately 35 yards for each sprint. You can vary the distance of the sprints to suit your conditioning level.
The idea is to never stop running or jogging. Do not walk back to the starting point in between sprints unless this is absolutely necessary. The ten sprints should be run in the following order:
1.Sprint from the starting point to the end point at full pace. Then without stopping turn around and jog back to the starting point…make certain you jog…do not run.
2.Repeat step 1 with another full pace, straight ahead sprint…jog back.
3.Now "sprint" using a side step. Using quick-paced sidesteps, "run" to the end point at full speed. Do not use crossover steps. Rather bring the feet together as you move sideways…jog back. Football players who play the line frequently practice this type of movement. Try to keep your body low in a somewhat crouched position as you do these sidesteps.
4.Repeat step 3 but this time turn around before you begin your side steps. Because you have turned your body around (if you were facing North in step 3, you are now facing South in step four) you will in effect be"sprinting" in the opposite direction…jog back.
5.Now, you sprint backwards making certain to stay on your toes and to pump your arms as you move. Be careful that you path is clear of any debris before you run this backwards sprint as you will not be looking in the direction that you are moving. Pay attention to when you have passed the end point. Stop. Then, jog back.
6.Repeat step 1 with a full out, forward running sprint…jog back.
7.Now we will do a sideways sprint as in step 3, but this time we will use crossover steps. A crossover step is when one foot moves in front of the other as you move sideways. Frequently in tennis we need to use a crossover step when we recover quickly from being pulled wide by an opponent’s shot. Don’ t be afraid to really try to move fast as you do this sprint…jog back.
8.As was the case in step 4, we want to move sideways, but in the opposite direction. To achieve this, simply turn around and do the crossover step . As was the case in step 4, because you have turned around, you are effectively moving in the opposite direction…jog back.
9.Repeat step 5…jog back.
10.Repeat step 1…jog back.
Granted most people are not motivated enough to do this nor do we have a spot really suited for this..