Don't feel as if you always have to be "on." Both you and your baby will have "down times" and you need to respect these moods by providing calmer, quieter activities.
Timing is everything. Your baby will be most responsive to your playfulness when she is both alert and unfussy. If you try to play when your child is hungry or tired or sick or upset, both you and she will gain nothing but frustration.
Don't worry too much about stimulating your child to give her a "head start" on learning. Just because you and your partner are your baby's first teachers doesn't mean that you have to put pressure on yourselves to teach her anything. Your child learns from everything in her world: the things she sees, touches, hears, smells, and tastes. She doesn't need a set of fancy flashcards or other learning aids, at least not yet. As you play with your infant, keep in mind that play is supposed to be fun. Both you and your child will have more fun if you keep the pressure to learn to a minimum.
During these first few months especially, what your baby needs from you is your love, your attention, and your time. More than anything else (even food), she wants and needs you to: