I use ABS only since my first 3d printer (mid 2013…) so i’m used to it a little
First,you need to do a proper calibration of your bed (if you can barely move one sheet of paper between your extruder and the bed, it’s good)
For the bed, you need a surface that stick… i never found something better than kapton tape cleaned (when cold) with aceton.
Your bed need to be heated to 105 -110 °c for several minute to be evenly hot (i used to wait 10 min)
Then the extruder come : depending of your abs AND your printer… for example,my solidoodle 2 underestimate the extruder temp…i use 185°c, my solidoodle 4 use 215°c and my i3 use 230 °.
In my opinion, your 250° are too much… even more if your extruder is not a full metal one. My rule of thumb is that you need around 50° more than the start of leaking of the abs from your extruder… start to heat your extruder, then Abs will start to ooze at a given temperature ( mine start at 160°c on my sd4) … add 50°c… and you will be in a good start range… wait one/two minutes to stabilise your temp and extrude something like 100mm of abs… it will ‘clean’ your extruder from old abs and set a good pressure in the head… then go… NEVER let your extruder hot without extruding for a long time (more than 5 minutes) or you will clog it…
Now for the software: the ‘BRIM’ (not raft) function is your friend… add 1 or 2 mm of Brim with one layer height to your piece… it will greatly help for the warping of the abs…
IF your bed if not flat enough, then you can add ‘raft’ to corrected this…
My slicer are set to print the first layer at 90% of the layer height
As Tanya said, an enclosure is a must to prevent warping … a simple cardboard box do the job. Cut a windows in it, and glue a sheet of transparent plexyglass/abs (to look at the print) and it’s good…
If you didn’t use an enclosure, prevent any movement around your printer when you print or your print can suffered from warping and /or delaminating
Depending of your filament, ABS smell are not good… use a well ventilated area (but no air movement near the printer)
I use repetier-host with slic3r at the moment… the last version is very good. The slicing of the last version is superior to cura/simplify3d IMO but it depend of the model…
EDIT : i made an error - i change skirt for BRIM (skirt is only to extrude some platic on the plate to load the extruder… a value of 1 at 3mm is a good value). use a value of 2 for BRIM to fight warping
add raft of 1 if your bed is not flat