Jupiter rules Sagittarius and the natural 9th House of long distance travel, academia and legal matters as well as anything associated with them, such as ethical, societal and cultural issues.  Jupiter is the largest planet in the solar system, which is also indicative of its astrological influence, which is primarily known for bringing good luck and considered one of the benefic planets in classical astrology.  Jupiter expands and magnifies anything it touches, generally in a positive way.

In transits to your Natal or Progressed chart, it will lend it's influence to those areas affected by the resident House.  For example, while in transit in your 2nd House you could get a financial windfall or in the 10th House you could get a promotion. 

In aspect with other planets, either natally or by transit, the results will be further colored by the other planets involved.  If the Sun, expect attention to be drawn to you or your accomplishments; the Moon, emotional issues; Mercury, communications will be expanded; Venus, comfort, beauty and affection; Mars, increased energy; Saturn, bureaucratic issues, responsibility or reputation; Uranus, unexpected events; Neptune, inspiration, intuition, fantasy; Pluto, introspections or obsessions. 

Again, house placements will further indicate which area of your life will be affected.  For example, in aspect to Venus with one or the other in the 7th House of relationships should bode well for your love life.  Naturally the Sign comes into play, also.  An aspect to Saturn in Cancer in the 5th House could indicate a change to a larger residence to accommodate a significant hobby/avocation or possibly the arrival of another child.

When Jupiter goes retrograde it draws attention to any need for reassessment regarding the Jovian issues previously mentioned, i.e. long distance travel, academia and legal matters.  Are the precepts still valid or is it time for some adjustments?  This will start at the global transit level and work down to you as an individual.  By transiting your own Natal or Progressed Houses, Jupiter retrograde could stimulate the Houses in the following ways:

1st House:  Is your personal integrity and value system in place?  Do you live by it?

2nd House:  Are your finances and possessions in order?  How important are they?  More so than people? 

3rd House:  Are your current thoughts and decisions in synch with your belief system?

4th House:  Is your neighborhood and home a true reflection of your deepest desires?  Does it represent you well?  Are you proud or embarrassed to live there?  Are you treating your family properly?

5th House:  Are you keeping to the same standards you teach your kids or are you a "Do as I say, not as I do" type?

6th House:  Are you honest in your work?  Are you comfortable with your employer, its standards and policies?

7th House:  Are your relationships as they should be?  Are honest with others and yourself?

8th House:  How self-serving are you when it comes to sex?  Are you self-sufficient in your finances or do you depend on credit cards or family members?  How respectful are you of life?

9th House:  Legal matters or property disputes could arise.  Will you handle them properly or exploit others?

10th House:  Are you comfortable with your reputation and community standing?  Do you care how you're viewed by others?

11th House:  Do you exploit others in your work environment or within any of your social circles?  Are your aspirations honorable? 

12th House:  Do any of your core beliefs require adjustment?  Are your a priori assumptions valid?