You need to prepare your merge document with conditional fields, that place
the information you want (and the following spaces) when the field(s) have
content and not when they don't.
e.g.
{IF {Mergefield Title} <> "" "{Mergefield Title} " ""}{Mergefield
First_Name}
the space is included in the condition
i.e.
{IF {Mergefield Title} <> "" "{Mergefield Title}<space>" "<no spaces>"}<no
space>{Mergefield First_Name}

Conditional field are coded by hand using CTRL+F9 to set the field boundary
pairs {}