In creating a conlang the hardest part of me is building a lexicon. Creating the grammar, the syntax, the phonology, and basically everything else is easier and more enjoyable than building up the word count. That being said it's impossible to do anything with a conlang without a variety of words.
When creating words I have a few methods. Sometimes I don't create a word unless I need it to write something in my conlang. Sometimes as I'm thinking about my conlang words simply come to me and I jot them down. This is a rare occurrence, and I wish it happened more. I also resign myself to sit down during my free time and create a few words. I never do that many at once to make sure I don't get burnt out.
When deciding what words to create there's a few things I reference. One is the Swadesh list, a list of a little over 200 words that are common to nearly all human languages. I still don't have lots of the words on this list in Reisu, so sometimes I pick out a few of the concepts and make Reisu words for them. Another thing I do is make antonyms for existing words. For example, I have the word 'larelai' for beautiful or pretty, but I don't have a word for ugly, so that's something I would want to create.
I then mull over the concept, and try to come up with how it would sound in the context of the other words I have. This is how I come up with most Reisu words. However from time to time I want to inject a little randomization into Reisu so that the words don't start sounding too similar to each other. In those times I use Awkwords word generator. After setting it up I generate about 100 words filtering for duplicates. I then read over the words and pick one from the list that hasn't already been assigned a meaning in Reisu and assign it the meaning I'm working on.
In the end I have a new word, or words!