This can be tricky and time consuming.
I sometimes Zoom in on the map and place the Table, chair,.. at the correct spot and this is off-set by a couple of MAP Feet or Screen Millimeters.
The Center of of objects are sometimes in the middle of the Questionmark "?"
So at times I have had things that didn't even look like they should be in building or tent but they were.
Also useful is the Set pos Script in the Intializ line of the Object:
this setpos [getpos this select 0, getpos this select 1,(getpos this select 2)+2]Now the Plus Two.. +2 ..at end is how many Meters the object being placed is up in the air or you can go negative numbers too. This helps in stacking things and placing items in the second floor of Buildings or below the building.
EX : Try a town with no city lights, put a fire[infalme true] in -3 (meters below middle of house) and Whoolaa house with Candle or fire place lighting. No need for Downloading Lighting Add-ons with this little gimmick.
Save this code You will use it a lot in making missions.
Hope this helps ya out