how do you increase your probability of winning?

The chance to win is random, so you should look for giveaways with less entries:

• enter groups (most have a level requirement)
• look for forum giveaways (some are hidden/you have to solve a puzzle first)
• do something awesome and get on people's whitelists

Edit;

• Not: create only region locked giveaways

Higher levels let you enter lvl restricted that have less entries but still the chance is low

Not really an answer to your question (others have answered that), but I recommend entering giveaways without any expectation of winning. That way you'll always be pleasantly surprised when you do actually win :)

since your account is already 2 months old, maybe you can consider applying for unlucky7 if you want higher chance of winning.

1. create 100,000 giveaways
2. poor users have no points to enter
3. mad probability gains