If you have a free living space (for example, the second apartment inherited), it can be leased. In cities such as Moscow and St. Petersburg, the cost of rent even for a simple apartment of economy class, located not in the most prestigious areas up to several tens of thousands of rubles per month. In medium and especially small towns, of course, rents are much lower, but too bad. The advantages of this option earnings minimum effort on your part. You just have to find someone who wants to rent your home. Disadvantages: the risk that the tenant will be unfair and then you have lawsuits.
Some people are now engaged in buying and selling shares. You can also try to earn money this way. Of course, in addition to at least some of the initial capital need to have skills in financial analysis. Seek professional help the mutual Fund (Mutual Investment Funds). If you can't go wrong with the choice Fund, under favorable market conditions can significantly increase the amount invested, and in a relatively short time. But, of course, that is not guaranteed, because the stock market is unpredictable, depending on many factors.
If you have good abilities in some science – get tutoring. Such services are always in demand, especially before the entrance exams to universities. A skilled tutor can earn quite substantial money. Of course, this again applies primarily to the residents of cities, especially in medium and small cities, the level of prices is much lower. But in any case earned money will not be superfluous.
You can try to start some small business or make crafts, writing articles to order. There are many ways. Importantly – be desire, imagination, initiative!