When speaking a language, one way to sound more natural is putting in those little linking words that give you time to think. Words like 'er' and 'um' are often used by English speakers, but there are others like 'well', 'then', 'so', 'okay', 'good' which have meanings but can also be used to some extent to fill a gap.
The same is true in Spanish, and learning these can give you the moment you need to choose the next word, letting you sound that bit more fluent. I've learnt a lot of these from listening to real people but also from podcasts, dialogue in books and TV programmes. Some of these are region specific so try to find out what people say in the version of Spanish you want to learn.
Some examples:-
bueno - good
pues - well
pues nada - well, nothing (used for a longer pause)
bien - well
a ver - let's see
entonces - then
vale - okay (in Spain)
dale - okay (in Argentina)
de acuerdo - okay (everywhere, as far as I know)
venga - come, come on
perfecto - perfect
vale, perfecto - okay, perfect