The obvious way to earn a second income is to get a part-time job. If you are not currently working, this is an excellent way to start as it gives you the freedom and flexibility to start other passive income opportunities.  The other option is to simply work from home full time which frees up commute time so you can focus on building more income streams.
I like the way you have listed the ways to earn extra income and was quite surprise that you did not make mention of network marketing, which is a way to make extra income without quitting your regular, though most people view mlm as a pyramid scheme but the real pyramid scheme is a regular 9 to 5, because you can only have one president of a company at any given time and network marketing business model to promote product that can be used is really cheap to join and can offer a substantial extra income or what do you think?
I would throw in some caution here: if your spouse works at the same company, or in the same industry as you, you are not diversified, and should something happen, you could be in a world of hurt.  Companies do go out of business, companies do lay employees off.  There is nothing wrong with working together, but realize that you are not diversified and you should be trying to maximize other income streams as a result.
California had a per capita income of $29,906 during the five-year period comprising years 2010 through 2014. About every third county and every third place in California had per capita incomes above the state average. Though somewhat counterintuitive, this implies that counties and places with per capita incomes even slightly exceeding that of the state can be classified as "high income" given the natural division of places into a top third (high), middle third (medium), and lower third (low) when ranked by per capita income. Hence, the upper third of all places in this ranking have a per capita income with a lower bound roughly equal to that of the state, about $30,000. The median place and county in California had a per capita income of roughly $25,000, and the lower third of both types of geographies had per capita incomes with an upper bound of about $20,000. Places and counties with the highest per capita income were concentrated in the San Francisco Bay Area, which has a relatively high cost of living. Those with the lowest per capita incomes were concentrated in the Central Valley, an economy in which agriculture assumes a primary role.
Liquid Funds are those mutual fund schemes which are ideal for putting money for a very short period of time, preferably not more than three months. Since these funds invest in extremely short term Debt papers, they come with very low volatility and risks. Accrual funds are those funds which invest in Debt papers of short and medium tenures to generate interest income. These funds usually do not take any interest rate/credit risk but stick to earning interest.
Note: A Tax Bulletin is an informational document designed to provide general guidance in simplified language on a topic of interest to taxpayers. It is accurate as of the date issued. However, taxpayers should be aware that subsequent changes in the Tax Law or its interpretation may affect the accuracy of a Tax Bulletin. The information provided in this document does not cover every situation and is not intended to replace the law or change its meaning.
No matter what venture you undertake in life, you need a team.  I’m a firm believer in team work, even if it is just to bounce ideas off of, or to have someone tell you that you are off track.  For many individuals, this person is their spouse, who also brings some income diversity to the table.  Just like I mentioned above, if your spouse has income, try to maximize it.
These days, low-risk bond yields aren’t enough to meet most income needs. When investing in bonds, the income typically comes as coupon payments – contractually guaranteed interest payments at predictable intervals.  There are many kinds of bond income available, so you must strike a balance between reaching for higher income (yield) and limiting risk.
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