Before you start, please take note of these warnings and comments:

• N.B. Make sure you are on lxplus6 or otherwise using an SLC6 machine. Make sure SCRAM_ARCH is slc6_amd64_gcc491.
• N.B. The setup script will check out many packages and take a while!
• N.B. You can ignore "error: addinfo_cache" lines.

Get everything you need, starting from a clean area:

cmsrel CMSSW_7_4_0_pre9
cd CMSSW_7_4_0_pre9/src
cmsenv
git cms-init
cd $CMSSW_BASE/src 
git clone https://github.com/cms-analysis/flashgg flashgg
source flashgg/setup.sh

Now if everything looks reasonable, you can build:

cd $CMSSW_BASE/src
scram b -j 9

And a very basic workflow test:

cmsRun flashgg/MicroAODProducers/test/microAODstd.py
cmsRun flashgg/TagProducers/test/simple_Tag_test.py

The setup code will automatically change the initial remote branch's name to upstream to synchronize with the project's old conventions.
If you need to commit, you'll have to put your username in the following:

cd ${CMSSW_BASE}/src/flashgg ; git remote add origin git@github.com:yourusername/flashgg.git