1.REALLY Learn the passage.
Here is an example. If you memorize three passages a week and keep this up for three years then you should know about 150 passages of scripture. When you have reached this point you may find it difficult to make progress because you have to spend too much time reviewing the verses you have done in the past. You may also find that you have forgotten the older ones and need to re learn them. (So you really do not know 150 passages) It may have been better to only do two passages per week and make sure that you know them very well before moving on. At the end of the three years you will find that you do not have to spend as much time in review. You can still recall the past passages and have time to move on to new material.
Part of the mechanics of memorization is to make sure that the passage is reviewed on a regular basis, many times at first but then with a larger and larger time interval between review sessions until all you need to keep it fresh is once or twice every few weeks
2.Memorize word for word.
It is important to be accurate. Just memorizing the 'gist' of the verse may be OK, but small errors can lead to misinterpretation of the meaning. If you are not careful, ideas can be lost or added to the passage you are trying to become familiar with.
3. Keep Trying!
The only real mistake you can make with scripture memorization is to quit.