Qazwsx linked a couple of documents designed specifically for this kind of thing. One is even the exact same as one that I'm recommending! I'll also give some detail as to why they're good and how they work.
Detect Balance
##Detect Balance ThisThis is a set of spreadsheets that uses a long list of different potential traits and bonuses (or penalties) that a race might have. The author has done some analysis of how existing races measure up within the ruleset, and given each trait (or bonus/penalty) a score. Adding these scores together gives you an average score.
The recommended score for new homebrew races is 24 to 27. Races should generally not eclipse 30 or fall below 20. - Detect Balance; Info.
In case you're not keen on adding a lot in your head etc, there is a calculator that does this for you in there as well.
This tool especially has been referenced by other homebrewers who have been very happy with the results. It's author used another tool (qazwsx's second link) but found it less precise than he wanted it to be (it's also not as interactive) so he built this tool, uses it, and playtests the results. There are oodles of comments from others who use it making tweaking suggestions to improve it's balance, too, so it's not just a theoretical document. What it lacks, however, is a homebrew class guide. Luckily the author of the other tool has been working on one...
5e Class Analysis/creation Toolkit
##5e Class Analysis/creation Toolkit WhileWhile still a work in progress, this guide is based on the author's experience creating homebrew classes (with at least one demo included) and has received some pretty positive chatter on his website. This guide is strongly reminiscent of Wizards of the Coast's own guide to tweaking existing classes, and includes details of how features and progressions in existing classes work, to help you model your own in a way that matches the existing system.
The class guide looks like it's more a tool to use from the beginning of your creation process, whereas Detect Balance (the first race creator guide) is really handy at any stage of the process, even just helping you know what to tweak once you've got something mocked up already.