Hi there -
The crucial thing to do is deposit a roughened layer of silver. This can be done by many methods depending on what equipment and chemicals are available to you. You can sputter coat a semi-rough silver layer just using a standard machine, but the surface will be quite contaminated and will oxidise very rapidly (it also won't be too rough). Alternatively, you can coat the slide using a wet chemistry method then roughen using electrochemistry.
The best way of fabricating a systematically roughened silver substrate is to use an evaporator and do what is called glancing angle deposition, where the substrate is held at a high angle relative to the silver source - this usually results in the growth of nanorods or pillars which give excellent SERS signals.
The final way is just to purchase commercially available materials - you can purchase colloidal systems or sol-gel's very straightforwardly. My company makes and sells Klarite, a commercially available solid-state gold SERS substrate. For reproducibility, any commercially available solution is likely to be much better than what you can achieve in your lab.
Finally, your choice of SERS substrate metal is of course determined by your instrumentation - silver will require a Raman instrument with a 514 or 532nm laser (maybe 633nm) while gold will work better at 633 and 785 nm.
Hope this helps.