• Where to Start, needless to say you will have to check where the puncher is on the tyre and if you can even fix it.  Providing it's a little cut or thorn your in luck. 
• Remove the wheel from the bike and start removing one side of the tyre using tyre levers if required.   To make it easer make sure your tyre is completely flat and the beed of the tyre is in the centre of the rim.  If using tyre levers Insert your first tyre lever on the opposite side of the wheel to your valve. This will give you the most slack and make inserting the tyre lever much easier. Hook the lever around the spoke to keep it in place and free up your hands.

 Insert the second lever no more than a spoke length away from the first and repeat with the third if necessary. Once you have enough slack, run the tyre lever around the tyre until you have one side of the tyre out of the rim.
• Check your tyre carefully for what ever caused your flat and remove from tyre.  If you can't find anything in your tyre inflate your old tube and check where it is leaking.  If its leaking from the inside of the rim you may have to replace you rim tape.
• Put just enough air in the new tube to give it some shape before putting it inside the tyre.  Once you have inserted the new tube, you can let some air out again. This will make easier to put the tyre back on.
• Position the tyre back on the rim making sure the valve is straight and work your way from the valve hole to the opposing side.  As you get close to getting the tyre back on it gets tight so time to get out the tyre levers again.  At this stage it is easy to pinch the tube so carefully lever the tyre on making sure your levers aren't in contact with the tube.  
• Last step,  If you have a CO2 inflater let it work its magic or if you don't start pumping. General guide for tyre pressure is run whats recommended on the side wall of your tyre

Cleaning your bike is one of the most simplest jobs you can do.  All you need is a bucket, warm soapy water, soft brush and a cloth.

Citrus cleaners are a good choice to help the environment too. 

• Using a stand (if you have one) hold the bike up, wash down with soapy water remembering not to spray directly at your bearings ie. hubs, bottom bracket etc.
• Brush clean the chain and cassette.  Once clean wash off detergent with water and dry thoroughly. 
• At this point it gives you a good opportunity to inspect for damage & cracks, last but not least remember to lube your chain lightly.