Memorizing the Holy Qur’aan is one of the greatest of blessings, because it is memorizing the words of Allaah, may He be exalted, that He revealed as guidance for mankind and healing for what is in their hearts. This decision of yours is a good one, and we ask Allaah to help you to achieve the good goal that you want.
Learning the rules of tajweed is important and will lead to correct pronunciation of the letters, improved recitation and avoidance of errors. But we do not think that you should stop memorizing. Rather you can combine the two and concentrate on reading what you want to memorize first correctly. It is best if you can learn from a woman who reads Qur’aan well. If that is not possible, then use recorded tapes and computer programs for memorizing and learning Qur’aan, and learning tajweed. It is known that the Prophet (peace and blessings of Allaah be upon him) did not tell his companions to learn tajweed before the reading and memorizing, but he did tell them to learn the Qur’aan from those who knew it well, such as Ubayy ibn Ka’b (may Allaah be pleased with him), Ibn Mas’ood (may Allaah be pleased with him) and others. This combined reading, memorization and learning tajweed.
Most people still memorize it in this manner; they start with memorization, whilst paying attention to correct pronunciation of the letters and learning the proper vowelling, then after they have memorized it or a good portion of it, they then pay attention to other rules of tajweed and the finer points thereof.
And Allaah knows best.