Without knowing your income and expenses, it is hard to give you a concrete number. That being said, your first place should be a 401(k),, providing that your employer has a diversified, professionally managed plan. If your boss matches contributions, always go for at least the maximum match (why not, it's free money). You can put more into your 401(k) than you likely can afford, but I would say 8-10% of your gross at current age and add a percent a year as time goes by.
I would also put some into a Roth IRA on the outside - you don't get the tax advantage on deposit, but it grows forever with not tax burden and you have more flexibility of investments than in a 401K, downside - you are subject to much lower limits on annual contributions (at your age, you can only put in $5,500 per year (about $450/month) . . . but this amount is completely separate from whatever you put in your 401K. Again, start out low, maybe $100 month, and index up from there.
Don't "save until it hurts", or you will quit. Instead, save until it feels good, build an emergency fund, save up front for major purchases, and make that retirement payment so automatic that you never think about raiding that account or cutting the amount you put in.
I call it Zen Investing == and like all things worth having, you have to commit to it.
| 10.30.15 @ 17:32