General Tips
Fully comprehending a scientific article will most likely take more than one read. Don't be discouraged if you don't understand everything the first time, reading scientific papers is a skill that is developed with practice.
Start with the broad and then to the specific. Begin by understanding the topic of the article before trying to dig through all the fine points the author is making.
Always read the tables, charts, and figures. These will give a visual clue to the methods and results sections of the paper and help you to understand the data. The author put these in the paper for a reason, don't dismiss their importance.
Don't be afraid to ask questions or look up definitions. If you do not understand a term or concept, do not be afraid to ask for help or look up an explanation.