1. If the subject is the activity, you must use "举行”， you can't use "举办”
他们的婚礼下个月举行。（* 他们的婚礼下个月举办。）
2. If the subject is person or organization, and the purpose of the activity is to present something to people, such as 展览会，展销会，画展，讲座，培训班，you must use "举办”， you can't use "举行"
3. If the subject is person or organization, and the activity is interactive, such as "会谈”，“比赛”，“联欢”，you must use "举行”，not “举办”。
4.When “婚礼”and“宴会” is used as object, both “举行”and“举办” are OK， but “举行” is more formal.
我们将在金色大厅举行欢迎宴会。 （我们将在金色大厅举办欢迎宴会。）
(more)他们的婚礼下个月举行。（* 他们的婚礼下个月举办。）
2. If the subject is person or organization, and the purpose of the activity is to present something to people, such as 展览会，展销会，画展，讲座，培训班，you must use "举办”， you can't use "举行"
3. If the subject is person or organization, and the activity is interactive, such as "会谈”，“比赛”，“联欢”，you must use "举行”，not “举办”。
4.When “婚礼”and“宴会” is used as object, both “举行”and“举办” are OK， but “举行” is more formal.
我们将在金色大厅举行欢迎宴会。 （我们将在金色大厅举办欢迎宴会。）