First Person Past Tense: I walked to the park and sat on the bench.
First Person Present Tense: I walk to the park and sit on the bench.
Combination Of Both: I walk to the park and sat on the bench.
I will happily read books in any kind of tense there is, so long as it's a good story. But when an author mixes tenses it makes me want to throw their book against the wall. Mixing your tenses this way is like mixing fire and gasoline. Only bad things can follow.
It can be hard to write in First Person Present Tense. I'm an author and I understand this. But if you find you aren't able to keep yourself in the present tense, then for the love of your book and its potential audience, please stick to past tense. You might have an awesome book, but if I get yanked out of the story every time you switch your tenses I'll never know it.
Images 1 & 2 courtesy of Master isolated images at FreeDigitalPhotos.netImage 3 courtesy of Stuart Miles at FreeDigitalPhotos.net