How can a non-IFR rated pilot fly SVFR?
In order to fly an SVFR clearance, the pilot and planned flight must meet several criteria.  The AIM 4-4-6 as well as 14 CFR 91.157 spell out the basic requirements:


You must have at least a private pilot certificate to obtain an SVFR
clearance during daylight hours as well as an instrument rating to obtain an SVFR clearance at night.  Student pilots are not permitted to request an SVFR clearance.
You must obtain an SVFR clearance to depart from Class E, D, C and B 
airspace if visibility is below VFR minimums. SVFR clearance may be prohibited in some Class D, C, and B airspace due to the volume of IFR traffic.  Check the airspace NOTAMs
for these areas prior to departure.
You must have at least 1 statute mile visibility on both the ground and in the 
air as well as remain clear of clouds (airplane) or simply remain clear of clouds and have at least 1 statute mile visibility for operations in Class B, C, and D airspace (rotorcraft helicopter).


All an SVFR clearance allows is for a VFR pilot to enter, depart or operate in controlled airspace using day VFR minimums for Class G airspace.  If it is done correctly by a competent private pilot and only in these conditions, it can be done safely as it provides the pilot with enough visual references to safely operate in VFR.  It is also advisable to do a realistic assessment of one's own abilities to control an airplane in marginal conditions and set conservative minimums for things like congested airspace or other weather in the area.  It is not advisable to do this if weather briefings anticipate IMC after departure.  Likewise if you have little experience operating in congested controlled airspace or if you struggle to stay ahead of the airplane under additional stressors, SVFR may not be advisable.