How to Express Your Feelings, 1689

Facepalm Cupid, Andrea Alciato, Emblematum Liber (1534)

Excerpts from The Theatre of Compliments, Or, A Compleat New Academy: 

Expressions of Love and Friendship of Men towards Men.
Sir, I'le repay your love with usury.
Sir, When I contemplate your perfections, I begin to abhor my self for my deficiencies.
Sir, Your great Virtues conquer all hearts as irresistably, as Alexander the Great conquer'd Kingdoms.
Sir, You alone can conduct me to the highest pitch of accidental perfection.
Sir, You have deserv'd more Services from me, than I am ever able to perform.  

Complemental Expressions of Ladies to each other.
Madam, I am forcibly carried away, (I know not by what fate, against the bent of my own Genius).
Madam, You have blasted the harvest of my hopes.
Madam, Nothing shall have power to alien my love from you.
Madam, In the intercourse of affection my love surmounts your's. 

Amorous Expressions of Gentlemen to Ladies, Gentlewomen and Maidens, &c.
Madam, Let the showers of your pity mitigate the fires of my fancy.
Madam, There's a civil assault within me, by which I feel a certain restraint of my own liberty and affections.
Madam, You have no more beauty than will serve to excuse you from being extreamly ugly.
Madam, Your hair negligently dishevell'd, and careless attire, grace forth your beauty; which shines in the midst of so many obstacles, as the Sun in a winter day. 

Expressions of Ladies and Gentlewomen to Gentlemen.
Sir, You are the emblem of terror, and your furious looks are able to consume a woman.
Sir, an ounce of give me, is better than a pound of hear me. 
Sir, I am like a bed of Roses where flowers are mixt with prickles.
Sir, I am not like the Dolphin whom the sound of Musick bringeth to the shore.
Sir, Farewel, you'r grown rude, I dare not hear you further. 

Need a quick sentiment for that greeting card? One of these lines will be perfect for the intercourse of your affection. 

How to Get the Girl, c. 1470

Your new online dating profile photo
Walters Art Museum, MS W.88, f. 40r (14th c.)

"Young men should not hate cats because they are the cause of great happiness and can assist in achieving success in matters of love with young and charming ladies." 

The Distaff Gospels 

This message brought to you by the 15th-century cat guild.

How to Maintain a Relationship, 15th century

Walters Art Museum MS W.166, f. 118r

"If a woman places feathers from a capon that has hatched young chickens in her husband's ear as well as hair from the right leg of his dog and from the tip of his cat's tail, he would never forget his love for her." 

The Distaff Gospels

The secret to a lasting relationship: just empty the vacuum cleaner in your partner's ear and you'll live happily ever after.

How to Enchant Your Lover, c. 1470

BL Stowe 17 f. 143

"When a woman wants to be well loved by her husband or her lover, she must give him catnip to eat: he will be so much in love with her that he will not rest unless she is close to him."

The Distaff Gospels

Even if this man-enchanting trick doesn't work out for some reason, you'll still be accompanied by a devoted band of cats.

How to Sweet Talk Your Lady, 1656

"Instructions for Lovers: teaching them, how to demean themselves towards their Sweet-hearts. You must not accost them with a shrug, as if you were lowsie: With, 'your Ladie', 'best Ladie', or 'most super-excellent Ladie': neither must you let your words come rumbling forth, ushered in with a good full mouth'd, Oath, as 'I love you'... But you must in fine gentle words, deliver your true affection: Praise your Mistress Eies, her Lip, her Chin, her Nose, her Neck, her Face, her Hand, her Feet, her Leg, her Waste, her every thing." 

Cupids Master-piece, or, The Free-school of Witty and Delightful Compliments (1656)

Some dos and don'ts for addressing your most super-excellent lady! Don't say "I love you." Do praise her various body parts. (Careful with that 17th-century spelling, though: it's her waist you want to praise.)

See here for more amorous compliments.