Read and comment on a paper in your selected field. everyone has their own style, but actively commenting while we read keeps us more deeply engaged. Write with pen, annotate a pdf, however you want to do it. If you're using an iPad, both GoodReader and iAnnotatePDF are good apps for annotations. If you have other suggestions for tools you like, please post them to the comments. 

Reading papers is a muscle and skill all its own. It takes practice, and is generally more time consuming than people expect. The goal is not to read as quickly as possible, it's to engage with the content and let it simmer and diffuse into the recesses of your mind. It is a very active process. Several people have written advice and guide to reading papers, and a few are included here that you may find helpful. These give a sense of the type of thinking one is generally being asked to do when consuming a prior work, as well as strategic approaches to peeling back assumptions and consuming new material. 

• "How to read a paper", in particular item 2, " Students' Resistance to the Time-on-Task Required for Deep Reading" 
• How to Read a Paper - Getting oriented (tareted at medical papers but very relevant to all areas)
• How to Read a Paper - the Three Pass Method (written by a computer science professor but field-agnostic) 
• How to Read a Paper - Quantitative Research (a great contrast between quantitative and qualitative methods, and reminder of the different value each brings). 
• Some more general pointers on questions to ask for reading papers (from a CS angle)

If you have the opportunity, it can be helpful to assemble a few people with similar interests who are willing to share readings, comments, and give feedback on yours. This could be an in-person meetup, a new group on P2PU, the Researcher's Homestead group on P2PU, or anywhere else. It does help to be reading papers at the same time as other people, but it's not at all necessary, and many of us do a lot of independent reading.  

As for the "when and how," try and set aside some time when you'll be undistracted for an hour or so. It helps to either print off the paper, or read in a digital environment that doesn't have pop-up notifications such as IM, twitter, email, etc. Tablets can be good for this. 

To complete this challenge, post your methods and (a link to) the annotated pdf  and/or a summary of the article to the comments. 

Now: simply repeat, at appropriate intervals, indefinitely :).