Three things to check first
Bonus size and qualifying deposits
Read whether the percentage is split over several deposits, what minimum deposit applies and whether a specific payment method is excluded.
Wagering and game contribution
Not every game may contribute equally to a bonus requirement. Check the promotion terms before you claim an offer rather than after you have started playing.
Time limit and withdrawal rules
Promotions can expire. Confirm the time allowed, any maximum-bet rule and whether withdrawals are restricted until the requirements are completed.
A welcome bonus should not change your budget. If the conditions are unclear or do not suit you, skip the offer.