Throughout each stage of your reading, keep you research question in mind. This will help you filter out information that you don't need while highlighting the information that you do need.
The abstract is useful for two main reasons: First, it provides just enough information to let you know if the article is worth your time. There is a lot of scholarly articles out there to read, find the ones that are most useful for you. Second, the abstract will tell you exactly what to expect from an article so you know what to look for as you read it.
A good introduction will tell you exactly what to expect, especially concerning the thesis or hypothesis. The conclusion will summarize the main points of the article. You can read it before the whole article because you don't need to worry about spoilers in academic writing. Once you have read the introduction and conclusion you will know the main point, arguments, and importance of the article.
Scientific articles in particular are likely to contain tables and graphs. Take the time to locate them and try to understand them in the context of what you know from the introduction and conclusion sections. This will better prepare you for all the dense information found in the article.
Once you have finished steps 1-3 you will be far better prepared to understand the article than if you read it just once from start to finish.
One of the best ways to find relevant scholarly literature is to pay close attention to which studies are cited in the article you are reading. By definition, these studies will be relevant to the information you just read.
Reading scholarly articles is different from leisure reading. The purpose here is not to be entertained, but to answer a research question. In the course of your research you may develop a long list of scholarly articles that you need to read and understand. The tips above will aid you in that process.