First check how many and which attributes are set to be used for search. To check this:
- Go to Stores > Attributes > Product
- Filter attributes based on Searchable = YES
Analyse and try to reduce the number of attributes being used for search.
Logic supporting above: Suppose you have description attribute set as searchable, then each word in the description will be treated as an individual keyword for search, even though you don't want it.
So try to use only those attributes enabled for search which you think are necessary.
Once you are done with reducing number of attributes from being searchable, do a reindex for EAV and CatalogSearch.
Hope this helps.