Finished my Mendel90 build and first test prints … success ! When printing PLA what should I be using to prep the glass bed ? Windex, alcohol or what else ? First prints stuck okay but then later ones didn’t ! Also as I am now ‘new’ to this is there a step by step proceedure starting with an .STL file ? I have Slic3r, pronterface and the Arduino software all working on Ubuntu 12.10
Soap/water. Avoid solvents if you’re using PLA.
I usually wipe down with water and a microfibre cloth between prints.
I print ABS exclusively on my Mendel90 (haven’t tried the sample of PLA nophead provided in his kit) - and find a dash of hairspray goes a long way - Bed temp is 130C (cardboard cover helps it get there quicker), extruder at 230C. Also, the cooling fan might be necessary for PLA, but it seems to just cause prints to come unstuck with ABS (bed heater can’t fight it - looking into building a heated build chamber.)
PLA loves blue painter’s tape. The cheap stuff. Wipe it down with a paper towel and try not to get your greasy fingers on it too much 
If you have a heated bed, 50-60 degrees is good for PLA - it’ll make it less prone to warping, and you’ll get great stiction without any binders.
Also, print the first layer slowly - 50% speed is what I usually do.
Top secret : watered down elmers glue.
Or a slushie of plastic and acetone. It’ll leave a thin film but it works arguably too well if even applied slightly too much. Its great for models you are seriously concerned with warping.
The acetone trick only works for printing with ABS. Blue painter’s tape on top of the glass surface works like a charm for PLA. Otherwise, just keep it clean, and make sure it’s warm enough. I find it works well between 50 and 60, but YMMV, since everyone’s thermistor is in a different place
Thank you all ! The Blue painters tape works great and @Ben_Van_Den_Broeck acetone trick is working out well too ! Now I can progress to optimizing slic3r settings on infill to build faster models.