Borrowing money to invest is an appropriate strategy, where the likely future performance of the intended investment type appears positive. When markets are performing well you will be likely to accelerate the growth of your investments at a greater rate than you would achieve if you only invested your current available funds. The interest you pay on the borrowed funds should be a deductible expense to you.
Margin lending allows you to borrow money for the purpose of investing in shares or managed funds. Margin loan facilities are offered by financial institutions and use part of the investment as security for the loan. Put simply, the facility gives you a loan to buy the investments which you want, within the range permitted. The amount which you can borrow is set at a particular loan to valuation ratio, and this is monitored on a daily basis by the lender.