Be patient.  Your dog is just like you, he will have good days and bad days, plus it takes time to undo bad habits!

Stay Calm.  Very important this one, if you get frustrated and cross with your dog he will not want to learn from you.

Start with something simple.  Starting each training session with something your dog knows well will give him a sense of achievement and will inspire him to pay attention.

End on a good note.  Regardless of how your training session has gone, always finish by asking your dog to do something he knows well.  This will boost confidence and a sense of achievement in you and your dog.

Pick a good time.  Trying to train your dog when he is over excited is almost impossible - likewise don't try to train him when he is half asleep.  Unless your dog is particularly greedy it may also be a good idea to leave it until well after meal times!

Use rewards.  This does not have to be a treat, some dogs prefer a toy or a cuddle but if your dog dog does like a treat, keep them small and keep an eye on his weight.  In fact, if you are trying to change your dogs bad habits you should rarely use treats - instead, think about what your dog is hoping to achieve with his bad behaviour and use that as a reward for the right behaviour, eg if your dog jumps up at you he is most likely trying to get your attention, so ignore the jumping up and when he does the right thing such as sit calmly, use attention to reward that, it will mean loads more to him that a treat.

Don't scold your dog.  If he gets it wrong then there is a reason.  Think about what could have gone wrong and work on that - maybe he just needs more practise, maybe the reward is not exciting enough or maybe he has become distracted, frustrated, tired, bored or over excited.  Stop the session and come back to it later, in the mean time try to think if there may be a better way to teach him what you want him to do.

Use a clicker.  This is a small plastic box that makes a clicking noise when you press on it.  After a couple of short training sessions (check the instructions for how to introduce the clicker) your dog will learn to associate the click with a reward and you can use it to reward him for any good behaviour - it will really speed up your training.

Be consistent.  You should be clear in your own mind as to what you are actually going to teach him and how.  Dogs can become easily confused and lose interest when you keep changing your mind over commands and techniques, so choose your verbal command or hand signal carefully and plan how you intend to teach him the new trick.

Teach one trick at a time.  If you are teaching your dog to sit then concentrate on just that until he has fully mastered it.  It is easy to get carried away thinking your dog is learning at an incredible rate and to move on to something else, but he will become confused as to what you want him to do and will not know the difference between different commands.  For the average dog I suggest teaching one trick per week, this gives you and him plenty of time to perfect it before you move onto something new.  

Keep training sessions short.  If you are trying to teach your dog a new trick, his concentration will start to waive after about 10-20 minutes and he may get fed up, you will achieve much better results if you have several short sessions as opposed to one long session.

Practise makes perfect.  As with everything, perfection comes with practise.  Once you have taught him something new, spend the rest of the week practising at every opportunity for example, before you put his lead on, before your feed him and before you pet him - this way he will also learn that he doesn't always get a treat but something good always happens when he does as he has been told.  Also, practise in lots of different places and with different distractions.

Be realistic.  Think about what your dog is physically capable of and consider his age too.  For example, many Greyhounds find the sit position very uncomfortable and a Great Dane may never learn to walk on two legs.  Watch your dog and the way he moves, his natural behaviour may give you a few hints as to what he may be good at.  Also, the older a dog becomes the longer it may take to learn a new thing - just be patient, he will get it in the end.

Keep it simple.  If you are training your dog to do something complex, then break the trick into small sections and work on one at a time, once he has mastered one section you can build on it with the next section.

Get help!  If you get stuck or are not succeeding, don't be afraid to ask for help from a professional.