Can I start a side business parallel to my job?

[ad8cents]

it depends on what is your definition of "earning something"

For most of the ppl, earnings from blogging itself requires a period of time and in small sums. Unless your blog gets recognised and u managed to get sponsors and high traffic.
On the other side, there will be people who would take the chance to pursuade u into internet marketing. Personally, I'm also in the midst of trying it out. But it seems to me it requires quite an amount of time put in (unlike wat the online ads' claim of "just 15mins a day")

You can check out my site for some ideas t8kethelead.blogspot.com
But I've got a feeling that you are looking for something more lucrative.
I suggest learning stocks trading or forex if you have time. But be warned of the risks involved.

[Brixton]

Yes, you can but I think you should do FX trading at FreshForex broker since they are now giving 300% deposit bonuses and many more lucrative bonuses like 1:2000 ratio leverage facilities.