Summary
The wise writer varies sentence structure and length to keep the reader's interest.

Sentence Variety and Transitions

If you followed my advice, you are now writing short, active-voice sentences. That's good. What's bad is that you can end up with pretty bland prose. For example:

No Variety


Bonds hit 73 home runs this year.  Bonds hit
all those homers from the right side.  Bonds
hit with power to all fields. Bonds hit low
pitches and high pitches, curves and fastballs.

Upside Every sentence is short and descriptive, active voice.

Downside Weak sentence variety. Every sentence has same subject (Bonds) and same verb (hit). Gets boring quickly.

Digression In a speech, repetition can be quite powerful.

Upside	Every sentence is short and descriptive, active voice.
Downside	Weak sentence variety. Every sentence has same subject (Bonds) and same verb (hit). Gets boring quickly.
Digression	In a speech, repetition can be quite powerful.

To enhance sentence variety, do the following:

Vary the subject and verb.
Combine tiny sentences to eliminate redundant subject and verb.
Throw in an occasional passive voice sentence.
Add transition words (next topic).
Invigorate the verbs.
Alter sentence length. After a few short sentences, add an occasional long sentence.
Alter paragraph length.

Variety

Bonds hit 73 home runs this year, all of them from
the right side.  Barry sprayed low pitches and high pitches, 
curves and fastballs to all three fields.

Variety

Bonds struck 73 home runs this year.  Batting
righty, he attacked a wide range of pitches with 
equal vigor.  Battling Barry hit with astonishing
power to all three fields.

Transitions

Good writers focus on transitions. Common transition terms include the following:

however
that is (don't use too often)
for example
nevertheless
unfortunately

Without Transitions	With Transitions
The C compiler can process 1,000 lines of code per second. The rate is slower when the host is fully loaded."	The C compiler can process 1,000 lines of code per second. However, the rate is slower when the host is fully loaded.
Commercial airplanes can cruise at altitudes up to 12 miles. The Concorde cruises at 60,000 feet. The Boeing 747 cruises at 39,000 feet.	Commercial airplanes can cruise at altitudes up to 12 miles. For example, the Concorde cruises at 60,000 feet. However, the Boeing 747 cruises at only 39,000 feet.

Transition No-Nos

It is tempting to start a sentence with "But" or "And." But don't do it in technical writing. And here's why: "but" and "and" are conjunctions, great for intrasentence transitions but not appropriate for intersentence transitions.