Not sure what you're having trouble with (probably reading the manual would be a good bet), but to run spectre from the command line you can do:

spectre input.scs

You can also use:

spectre -h

for help (if you don't want to read the full manual).
Of course, you'll need to have some of the RF analysis
statements in the netlist - you can always take a look
at the netlist you get from ADE.

The problem tends to come if you want to use some of the more advanced post-processing methods from ADE. If you're running standalone, not all of them would be easily doable, so you might be better off writing an OCEAN script to run the simulation and process the results that way. See the OCEAN manual for more details.

Unfortunately because your question was rather vague, I feel my answer is similarly vague.

Andrew.