We get this question a lot, but the answer to this is never simple. There are factors that should be taken into consideration before seeing any improvements on your rankings, let alone before commencing any SEO work.
Factors to consider include the age and current condition of your website and its current Google ranking, the content itself and competitiveness of the keywords used, backlink profile, and your competitor�s current position, amongst many others.
That said, an SEO campaign involves strategic, long-term planning and execution that takes up several months to accomplish. Generally, positive movements may be achieved from the 6th months onwards.