For Silver Spring, if you take Rock Creek Trail you'll need to switch to Beach/Jones Mill at E/W Highway. Where the Capital Crescent / Georgetown Branch crosses, go right on the CCT over the trestle bridge. Where the trail ends, go left and right on Brookville. T's at Seminary a couple of blocks from Georgia Ave and downtown SS. Or follow the Bike Washington map
http://bikewashington.org/trails/cct/cct.htm
RCT may be a bit out of the way from Capitol Hill. Georgia, 13th or 16th all more direct.
You could always wait for the Metropolitan Brach to get finished.
http://bikewashington.org/routes/dcloop/dcloop.htm