I'm just starting GTD and using Evernote to manage my tasks.
Have you looked at the Evernote Set-up guide from here? I am sure that will help with basic setup.
When processing your Inbox, how many items do you move to various contexts? Just those you plan to work on soon or everything that fits?
Only move to contexts those things that are not Someday/Maybe. I personally like to work with long lists and lots of choices. Plus most of my work is seasonal. So I typically have on my lists as active projects anything I can do in the current 3 month season. That means that for me I usually have about 200+ active current projects, and about 300+ actions defined for them spread across 37 active contexts.
When I process my inbox if the item is something related to a current active project I add it as applicable, it might be support material for that project, or it might be an action but it goes on my lists. If it's part of a someday/maybe project I will add it to the project support material for that project if I have created a folder for it or if not I might just add it as a note under my Someday/Maybe lists. I keep my S/M items in DEVONThink but it's similar to Evernote.
As an example: I write blog posts on various topics and the topics come to me at different times. It's usually helpful to compare one topic to another to prioritize. If I only put the one I plan to work on right now into @Work PC , and the rest into Someday/Maybe, it would make that comparison difficult.
The way I would handle that type of thing is that I would have a single active project called "Blog Updated Weekly" with the action of "Write this weeks' blog post" in the context Scrivener (my writing tool of choice) and in the notes for the action I'd say something like "See list of possible topics in DT note Blog_Updates. My DEVONThink note would have a list of all my blog topics that I had thought of, just a plain text file like this:
Discuss options for setting up a chicken brooder in an old water tank
Explain my scoring system for sheep evaluations
Describe my Lamb Bag contents and how I use it
Why you should eat rare breeds to save them
etc. etc. etc. for all the various ideas I have had about the blog
Then say I am processing my inbox and I come across a note I scribbled that said "blog idea custom vaccine notes" That would translate into a line in my DT note for blog ideas "Explain how we created a custom vaccine for Clostridia Type A for our flock".
Now it's my blog day and I need to create an entry. I look at my action lists for the context Scrivener and see that I have 3 things to do, one is write this weeks blog post. I reference my list and I decide that the one I want to actually work on now and get up or at least written is the one on eating rare breeds because it's fall and that's when we slaughter and I want to drive more meat sales. I delete it from my DT note, add it as a post in my blog document in Scrivener and start writing.
And in fact that is exactly the structure I am in the process of implementing for myself because I am woefully out of date doing my farm blog and really need to write blog posts more frequently than once or twice a year! ;-)
Does that help?