How does Browning use literary and poetic techniques, in "My Last Duchess" and "Porphyria's Lover" to effectively convey his views and ideas?

Numerous answers to your question could be given.  Far too
many for a short-answer format such as this, in fact.  I'll give one
answer.

Browning's use of a first-person
speaker in both poems allows characterization
to be revealed about those speakers.  The speakers indirectly condemn
themselves, at least from a reader's point of view.

In
"Duchess," the speaker's pomposity, arrogance, self-importance, and egocentricity are
revealed by the speaker's words.  When he lists people and actions and animals and bits
of nature (imagery) that brought joy to his deceased wife,
and lists these as the behaviors she exhibited that led him to order her to be killed,
he reveals his true nature and personality.  This allows the reader to "discover" the
Duke's personality and character, and draw his/her own conclusions.  The
dramatic monologue form, including the silent listener (a
representative of the father of the Duke's new fiance who, in effect, is being
threatened by the Duke), provides the occasion for the Duke to indirectly reveal
himself.  The listener's silence, of course, also reflects the Duke's personality--he's
not one to let others talk.  His ideas are the only ones that
count.

In "Lover," the first-person speaker
reveals his personality (characterization)
in much the same way.  Again, the speaker is unaware of the reaction a reader will have
to his narrative.  He describes a moment of beauty and purity.  As he explains the
moment of Porphyria's true and pure love, and how he captures it and maintains it, he
inadvertently reveals his warped and egocentric mind.  Porphyria brings to the scene
peace and calm and love and purity, and the speaker sees his act as in line with peace
and calm and love and purity.  She dies, he is sure, without pain.  Pain would destroy
the moment, so he refuses to accept or acknowledge it.  He reveals his deranged
mind.

First-person speakers allow Browning to reveal
characterization indirectly through unaware narrators.  First-person speakers allow
Browning to let the speakers condemn themselves, and to let readers discover that for
themselves.