The first stage of any carbon reduction program is an initial analysis, historically this has normally been a scope 1 or scope 2 analysis.
Scope 1 is your travel and electricity/energy use
Scope 2 is electricity/energy used by 3rd parties for your organisation.
The problem with this is that it does not cover the majority of your organisations carbon footprint. There are a few organisations such as power generators or aluminium smelters where this may be the majority, but for most organisations the travel and energy use is a small part of their overall carbon footprint, and the majority of the carbon footprint comes from the other goods and services that the organisation uses.
The analysis is the start of a proper carbon reduction program, where the highest areas of carbon usage are identified projects created that have the maximum cost benefit in reducing the organisations carbon footprint.
Carbon reduction should be carried out before looking at carbon offsetting, since carbon reduction will normally provide you with organisational savings and offsetting creates additional expense. You could use the savings generated from carbon reduction projects to offset those parts of your organisation that can not be cost effectively reduced in emissions.