• if you have a I chord that doesn't sound right, try iii or vi instead
• identify target chords (first chords of phrases are good opportunities)
• give them their own ii-V (or just V)
• you can either borrow time from the previous chord, or replace it entirely
• always pay attention to the melody
• inversions can be used to create stepwise bass lines
• secondary ii-V's can even get their own ii-V's

Other resources:

• Harmony and Chord Progressions / Secondary Dominants: Triads, Seventh Chords