absolute minimum wire and pad sizes for hand-made PCB's
With regard to size of tracks, and in terms of the home PCB production equipment itself, I would recommend 0.25mm as the absolute smallest size that you can (reliably) get away with.  But I tend to stick to >0.3mm if I can.

Unfortunately this minimum size is dependent upon high quality transparency prints.  To achieve 0.25mm I use a 1200DPI printer.  You will struggle to do this with a 600DPI printer.
If the printer is your limiting factor, then this will usually be obvious from the printout itself.  So you can try some different track sizes and see what the minimum reliable print is.  When testing, group a bunch of the tracks together as that will show up the limitations of your printer much more obviously.

Regarding pad sizes, well, this limitation is defined by the part you're designing into your product and not by the capabilities of home PCB production.  Look up the datasheet for the part and you should find a recommended footprint for it.