simply double the number that you're multiplying. for example, 2 x 4 = 8. that's the same as 4 + 4.
multiplying by 4: double the number you're multiplying, then double it again. for example, 4 x 4 = 16. that's the same as 4 + 4 + 4 + 4.
multiplying by 5: count the number of 5s you're multiplying and add them up. use your fingers to help count if you need to. for instance: 5 x 3 = 15. that's the same as 5 + 5 + 5.
multiplying by 10: this is super-easy. just take the number you're multiplying and add a 0 to the end of it. for 