Both ways can work. Looking up words, and trying to guess the meaning from context. I use both, depending on my mood and the situation.
I like trying to guess the meaning because you have to think things through. That helps you remember the answer. Doesn’t matter if you got it right or wrong. It’s not always easy, but it gets better with practice.
You can usually look at the situation and narrow it down to a few possibilities. If my guess seems decent enough to get the gist, I keep going. Usually, you’ll find something that helps you figure out if you were right.
If I see a word several times, I usually look it up. Otherwise, it’s probably not that important (unless I happen to be curious).
And if I look up a word and forget it, no big deal. Happens all the time. I’ll either come across it again, or it wasn’t that important.
It can be slow going, no matter what option you choose. But if you keep at it, you can get to a point where you rarely have to look things up.