Vlad already mentioned some resources you can use for practice; in terms of the general approach for the analysis, I would recommend the following steps:
1. Read the graph
- Ask for one minute of time to understand the graph.
- Summarize what the graph is about. Read in particular the graph title (often forgotten), the axes and the legend.
2. Analyze the graph
- Repeat the main question you have to answer. Many people don’t spend time to clarify the specific question they have to answer; consequently, they answer the wrong question. Don’t be one of them and be sure to restate what is the main insight you have to derive
- Provide an analysis related to the question. Once you have a clear understanding of the graph, then, and only then, you can move to an analysis of how the graph can answer the question you have repeated.
3. Provide a conclusion for the graph.
- Answer to the question asked. Again, very often people simply state what the graph is about, without providing any conclusion. A great candidate will provide a connection between the analysis done and the previous question formulated, with a clear summary of the whole analysis
- Present the next steps to follow based on such conclusion. As a last step, a great candidate will present what can be done next to help further the client on the particular question asked.
Hope this helps,