The title and section headings of the paper give you a basic understanding of what the paper is about. They also help you get a feel for the structure of the paper and how it's organized.  Take note of any sections that appear longer or denser in relation to the other sections of the paper. It may take more of your time to read through those. The title and the section headings also give you an idea of whether the paper is relevant to your interests and how difficult it will be to comprehend. If the title and section headings include terminology you don't understand, you may want to do some background reading and then come back to it. The abstract is a summary of the paper as a whole. It will tell you what questions the authors sought to answer, the experiments they conducted, and the answers they found.  Typically you can access the abstract of a paper, even if you can't read the whole thing. For example, you may find an article published in a journal you can't read without a subscription. The abstract will let you determine whether the full article is something you should read. If after reading the abstract, it doesn't seem like the paper would be beneficial for you to read, there's no need to read any further. The introduction places the paper in context. It will let you know what is already known about the general topic, and how this paper fits in with the broader line of scholarship.  The introduction gives you a little more information about the questions the authors sought to answer, and how those questions fit into the larger field of scholarship. If the paper falls into a field of study that you're not familiar with, the introduction may point you towards resources you can use to gain enough information to properly understand the paper. If you're not familiar with the topic of the paper or the questions the authors are trying to answer, you may need to do a little background reading before you'll be able to understand the paper.  For example, if you're confronted in the introduction with a lot of terminology you don't understand, look for a general overview or review article that will provide you with the background you need. You may also want to use scientific dictionaries or other reference books to get a better understanding of words and phrases you aren't familiar with. Reading the conclusion before you dig into the meat of the experiments gives you a better ability to analyze the data and evaluate the data in context. Skip forward to the end of the paper and read the conclusion section that summarizes the authors' findings.  Take note of the conclusions the authors made so you can refer to them as you read through the data. If you don't understand the conclusion, you may want to do additional background reading before digging into the data. Assuming you've gotten this far and have decided that you need to read the paper, move forward to the paper's methodology section. If the authors used a method you're not familiar with, you may want to do a little background research on that method before continuing.  Make sure you understand what the authors did, and how they did it. Look for potential holes or biases in the authors' method. If the method doesn't seem like the best possible method to answer the questions, compare the methods you thought would work better. Jot down why you think your method would work better than the method used in the study. Most scientific papers include tables, charts, and graphs that summarize the data collected in the study. These figures allow you to look at all the data together and form your own conclusions on that information.  Depending on the methods used, the figures may allow you to analyze the data more easily than you would by simply reading the paper. By looking at the figures, you get a general idea of how the study was conducted without even reading the paper. Think critically about the way the data is presented in the figures. Ask yourself if the data could have been represented in a clearer way. You can also consider if the figures chosen represent a bias on the part of the authors, or if they are attempting to present the data in a way that supports their conclusions. Once you've looked at the figures, dig into the narrative sections of the paper that present the data and describe how it was gathered. Look for potential flaws in the gathering of the data that might affect the results.  Typically, the authors use the text to highlight the data they felt was most important in the study. This is the data they used to support their conclusions. Compare the data described in the text with the data in the figures. Ask yourself if they left out important data that may have led to a different conclusion. The data may raise additional questions not discussed by the authors. Formulate a hypothesis as to why that data was ignored. After focusing on each section, read the paper actively. Take notes in the margins or on a separate sheet of paper as you read. Highlight or underline key phrases in the text.  Be on the lookout for words such as "surprising" or "unexpected," which will give you clues as to how the authors interpreted the data they gathered. Phrases such as "in contrast with previous work" or "has seldom been addressed" help you put the paper in the context of the overall field of scholarship. Words such as "propose," "suggest," or "hypothesize alert you to conclusions the authors are making. They may also point to unanswered questions that invite further research.

Summary:
Glance over the title and section headings. Read the abstract to determine whether the paper will be useful for you. Continue with the introduction if the paper seems relevant. Review articles about the topic as necessary. Look at the paper's conclusions. Study the materials and methods sections carefully. Evaluate the figures included in the paper. Read the narrative sections that discuss the raw data. Go through the whole paper again from beginning to end.