Here are two really simple types of transition you might use in your development.

Parallel thirds (or sixths)

One of the easiest ways to move from one key to another is to strip down the texture to thirds and sixths. The first example starts in C major and uses parallel thirds in the violins to modulate to G major. You need to use your judgement, avoiding the notes that change in the first few thirds and then making it go smoothly into the new key.

• Start with a third that fits with the tonic of your first key
• Write a series of thirds that leads onto chord V of your new key. It is important you start using the new accidental (here F#) straight away
• Resolve your last third(s) that fit with the new chord V onto the chord I in the new key
• This is about as short as will probably work. You can extend by adding in more thirds

The second example goes from A minor to F major. This involves TWO changes of accidental so it takes a bit longer to achieve smoothly. It is just a matter of delaying the new notes the right amount of time.

The second example uses a pivot chord from a major key to a related minor key.

Pivot chord

This is just as in your transition – you use a pivot chord to get from one key to the next.

• Start with the tonic of the first key
• Write a progression that leads to whatever chord in your first key is also the tonic in your new key (here E minor which is vi/i)
• Follow this new tonic with a perfect cadence in the new key (remember accidentals)