Every German noun has a gender, and there is no way to guess it every time. The good news is that a few habits make it much easier, and the genders you meet most often become automatic with practice.
1. Learn the article with the noun, always
Write and say die Lampe, never just Lampe. The article is part of the word, not an extra. If you learn a noun without it, you will have to look it up again later, which costs far more time than learning both together at the start.
2. Give each gender a colour
Pick a colour for der, die and das, and use it every time you write them down. Many learners use blue, red and green. You will start to see the colour in your head when you recall the word. The vocabulary tables on this site colour the articles in the same way for German.
3. Use the clues, but treat them as hints
Word endings give you a good first guess: -ung and -keit are feminine, -chen is neuter, and days and months are masculine. They have exceptions, so use them as a guess and check the result. There is a full list in Der, die or das? Clues to a German noun’s gender.
4. Learn short phrases, not single words
A small phrase carries the gender with it, and often the case as well. Mit dem Zug tells you that Zug is masculine (or neuter) and that mit takes the dative. Ein schöner Tag has the masculine -er ending on the adjective. The phrase comes back to you whole, and it sounds right when you say it.
5. Say the article before you check the answer
When you test yourself, say the article out loud before you look at the answer. Guessing and then being corrected helps the gender stick better than simply reading it. On the vocabulary tables on this site, cover one side, and try to say the whole word, article included.
6. Don’t panic about mistakes
Everyone learning German gets genders wrong, and people will nearly always understand you anyway. A wrong der or das is much less of a problem than not speaking at all. Keep going, and the genders you meet most often will settle first.