The form ‘used to’ in English is our ‘solía’ in Spanish. It goes only in the past simple (used, didn’t use) followed by   to- infinitive (I used to go) and it expresses a habitual action in the past.

Follow you have a printable document with all the information needed to form it well as well as some exercises.
USED TO.doc
If  you click here, you can find form and uses of ‘used to’

If you want to practise online, try the following two exercises:
Exercise 1
Exercise 2

Maybe you have a lot of free time for practising. In that case, try this link. There  you will find lots of links to different exersices. Be careful and make sure that you are practising something you have studied!!