Try first to look at the word you are working with, and see if all the sounds are in the word as you say the word. 

For Example:  stamp-  you can hear all parts of this word. 

If there are parts of the word that are not "heard" as you say the word, start by thinking, focusing- on those parts.

For Example:  chain-  the i sound makes the A say it's name. 

       to remember the i  - think of a chain in an i shape, or try saying a silly sentence such as;

"I made a chain out of eyes". 

Later, see if the silly sentence or the vision of the chain made into an i works, and you can remember the word.

Another approach is to try coloring the word so you can remember the shape of the letters better.

Still another system is to pay close attention to where you have made the mistake.  If you spell the word they as thay, notice the place you went wrong (you wrote an a, not an e!).  When you practice the word , write the letter you goofed on really big, like this:

thEy.  When you go to write it, shut your eyes and try to remember what letter you wrote very large. 

There are many many tricks to learning how to spell words.  If these do not work for you, ask me and I will give you more.  The worst thing is to write the word over and over and over again.  If you copy the word ten times and don't learn the word, copying it fifty more times might not work either.  Use a different  tool to get the job done.  I always say, if the horse is dead, you don't get a stronger whip to make it go, you get a new horse.  Keep at the word with different approaches, and you will win!!