There are several ways to jack up and secure your 993 for those DIY projects.
Before you start I recommend you not try to save any money in buying cheaper off brand jacks, jack stands or floor jacks. When it comes to buying equipment or tools that may jeopardize your car or your safety always buy the best. Sears is a good place to buy the jack stands and floor jacks from. I am sure there are other places to buy these things from, but you will need to look around on your own.
When buying a floor jack make sure you buy the model that has a removable cup, when jacking your car up with a floor jack that has the cup on really put more stress on the contacting point. (Hence all the weight is on the small lip area) I remove the cup off my floor jack and just use the flat area underneath the cup. This way the weight is distributed over a larger area and less damage will occur to the jack points on your car. Also if your car is lowered, there is no way for you to get the floor jack underneath the car without removing the cup.
Most importantly! Always use a jack stand!
Personally I do not place the jack stand underneath any suspension pieces or anywhere that is not originally designated as a jacking point. I am sure there are several other places to place the jack stand on the 993 which will not damage the car what so ever, but you can make that decision on your own.
There are 3 different configuration you can have your car up in the air.
Just the front
(1). Just the front - Lift the car up using the floor jack on the rear jack point of the car, and place a jack stand underneath the front jack point and lower the floor jack. Same for both sides
(2). Place the floor jack underneath the engine crankcase, (you can only do this if your soundtray,engine under cover,or engine tray what ever it is called have already been removed) jack rear of the car up to the height you desire and places the jack stand underneath the rear jack points and slowly lower the floor jack.
(3). Do procedure (1) first and then (2).
picture shows the rear jack point of the car
picture shows the rear of the car resting on the jack stands
pictures shows the spot where to place the floor jack under the rear of
the car underneath the engine