One of the goals of lojban was to create a language with unambiguous grammar. The idea was to create a language unambiguous enough that a computer could read it successfully.
This is largely achieved through the predicate logic of the language, specifically with the place structure each bridi is assigned, and by drawing attention to those ambiguities that cannot be eliminated.
The place structure based predicate system that the bridi use is at the center of the attempt by the makers of lojban to reduce and clarify ambiguities. As an example, the word tavla has the following place structure
x1 talks to x2 about subject x3 in language x4
If a speaker says
Although the person the speaker is speaking to is not mentioned, the place structure indicates that there must be an x2 for x1 to talk to, and likewise you must have spoken about some subject x3, and in some language x4. The place structure was created to run in order of importance based on the bridi and the subject with which it deals. The presence of such places in the bridi make their exclusion in the utterance obvious; even if they remain unstated. Thus, although ambiguity remains, the ambiguity is noted and does not slide by as it might in another language.
Lojban further augments the bridi place structure's unambiguity by requiring a marker to denote figurative speech (pe'a). This means that any metaphors or other figurative language is marked, thus preventing the confusion normally common when a listener does not realize that a statement is meant figuratively or misinterprets the intended meaning of the figurative language.
All of Lojban's punctuation is spoken and written out, preventing the errors possible in English when a comma or period is removed or added in error.
The lack of default gender or tense superficially seems to add to ambiguity, but has the actual effect of limiting ambiguity, because nothing is assumed regarding these things before hand. As with place structure, ambiguity is not removed, but highlighted. The speaker knows that an event must have taken place during a particular time or place and that certain nouns should have genders assigned to them, and is free to request more information about the tense or other modifiers since they are not assumed to be a default- such as the present or male (as in the case of gender).