Well, that's a very good question. Bible contains several verses to understand how often should we pray, how long should our prayers be, etc...
Let's consider on a first hand Matthew 26:41 :
Keep on the watch and pray continually, so that you may not enter into
On first reading, one might think we might always pray, that's it : continually.
This could be confirmed by Romans 12:12 and even 1 Thessalonians 5:17, that encourage us to "persevere in prayer" and "pray incessantly". Other reference are Ephesians 6:18
However, these statements do not mean that we must be praying God every moment of the day ! Rather, the Bible is urging us to pray regularly, continually thanking God for his goodness to us, looking for his guidance, comfort and strength. Indeed, if we truly appreciate the privilege of prayer, we will find many opportunities to pray our heavenly Father.
But of course, we should use this privilege with wisdom, as there are several conditions for prayers to be accepted by God. So we may pray for anything that is in harmony with God's will, as we can read in 1 John 5:14 :
And this is the confidence that we have toward him, that no matter
what we ask according to his will, he hears us.
But, as this topic(What may we pray for ?) could be covered in an entire post, just remember we can't pray for anything.
So, if we need to talk to God, ask him something according to his will, He will ALWAYS listen. There is no limit, no quota, when it comes to speak with our heavenly Father !