First of all, STOP having late payments!!!  Do not have any more late payments whatsoever.  Each late probably drops your score by 20 to 50 points - no joke!!

Next, pay down your credit card balances to 30% or below the available credit limit.

If you are over your limits, get those ones down the quickest.

Pay off all non-medical collections as soon as possible.

If you do not have any credit or trade lines established (i.e. - loans or credit cards) then think about getting a small secured credit card that reports to all 3 bureaus.
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If you're in serious debt, think about a free Debt Reduction consultation: http://www.curadebt.com/freeconsultation.asp?a_=4b75ef9e10138

Be patient.  Over a year or so, your credit will come up.  Also, having an installment loan and revolving credit will help.

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