I am not sure if everyone is aware about what creates lag. Pls fill in the gaps if you know more issues :-). But for me, in the past I used a lot of prims. Using more than 3000 prims on one region can make it laggy. Even, make the objects phantom if possible, which will keep the serverusage better. Then, bad scripts. Most SL scripts are old and have a heavy usage. And also very important; the textures. If you import textures, try to reduce them to no more than 1000 pixels. I use mostly 500x500 and edit them in Gimp, a free tool. Above that number the viewer even won't import them. It will keep the use of your content mostly free from lag. Last: using a cableconnection instead of wifi helps a lot, your usage goes a lot faster and sometimes HG doesnt work for visitors.