Sort out the financials first of all guys.
For example, it is not acceptable to pay your rent late, as the rest of the flat has to deal with it through either the landlord paying a visit or an automatic payment not going through which could cause extra bank fees.
If you can''t pay something on time, tell your flatmates before rather than after and sort out some sort of arrangement with them. If it''s about paying rent, unless you have a very rich flatmate none of them are going to be very accommodating of your situation. Would you want to pay your flatmate''s rent if you know they can''t afford it in the first place?