One feature I love on Ravelry, if you have your stash logged, is when viewing a pattern, there is a link to yarn suggestions and it will show you what you have in your stash that might be suitable for knitting a particular pattern! Genius!
While picking the yarn is a task in itself, choosing which pattern to knit can also be a task. I love this stash feature to help me hone in on how I can stash bust, but if I am going to invest the time knitting, I want to pick the right pattern.
I also help a lot of folks out with their knitting patterns - you can get help from me too! Submit a help request or join us over on Knit Chats for round-the-clock knitting and crochet help!
Read the whole pattern first. Just like cooking from recipes, I advise my knitting students to read through the entire pattern before casting on or working up a gauge. While it can be tricky to determine if a "pay" for pattern will be worth it ahead of time, there are several clues that can point you in the right direction. Learn about essential pattern elements. Read more about the elements I consider essential to good knitting patterns here. Most patterns contain mistakes. Ultimately, it is best to assume that all patterns contain mistakes, or that you will make a mistake or get confused at some point. It's important to know that THIS IS NORMAL!
Reading knitting patterns is like reading in another language. Not everyone finds it as fun as I do!
Stretch yourself, but not too much. So if that is the case, take the time to acquaint yourself with the essential pattern elements to look for. Maybe start by reading the list of abbreviations or special instructions translated in a pattern. My general rule of thumb for beyond beginner or knitters looking to gain more skills, is to only choose a pattern that contains 1-2 new stitches for you. Go beyond that and it might get overwhelming. Just like with recipes, where you make sure you have or can make all the ingredients!
Look up errata before you start. It's also a good practice to make sure that the pattern exists on Ravelry. This makes it easier to find any posted errata (known mistakes from the author and fixes). You can also search pattern websites but if the patterns are out of books or very old, you may be in for more of an adventure. Use caution!
For the love of photos. One thing that is a clue you might be looking at a decent pattern is if it contains lots of photos. Depending on what you plan to knit from the pattern, the more complex, the more photos you will want. This can be especially helpful to debug (sorry, coder term!) any strangeness that comes up, or hard to interpret instructions.